Short-Form 5G/6G Pulse-Amplitude Demodulation References

ABSTRACT

Short-form pulse-amplitude demodulation references disclosed herein may enable low-cost receivers to demodulate wireless messages while avoiding complex 5G and 6G protocols, thereby enabling a multitude of cost-constrained applications. Despite their small footprint, the short-form pulse-amplitude demodulation references enable the receiver to determine all of the amplitude levels of the modulation scheme, including the effects of noise and interference. Mitigation of noise and interference can therefore be provided by embedding short-form pulse-amplitude demodulation references within longer messages, thereby providing an immediate refresh of the modulation calibrations, enhancing communication reliability, and avoiding costly message faults despite high background interference. Short-form pulse-amplitude demodulation references disclosed herein can be used as a default standard demodulation reference in 5G and 6G wireless messages.

PRIORITY CLAIMS AND RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 63/210,216, entitled “Low-Complexity Access andMachine-Type Communication in 5G”, filed Jun. 14, 2021, and U.S.Provisional Patent Application Ser. No. 63/214,489, entitled“Low-Complexity Access and Machine-Type Communication in 5G”, filed Jun.24, 2021, and U.S. Provisional Patent Application Ser. No. 63/220,669,entitled “Low-Complexity Access and Machine-Type Communication in 5G”,filed Jul. 12, 2021, and U.S. Provisional Patent Application Ser. No.63/234,911, entitled “Short Demodulation Reference for ImprovedReception in 5G”, filed Aug. 19, 2021, and U.S. Provisional PatentApplication Ser. No. 63/272,352, entitled “Sidelink V2V, V2X, andLow-Complexity IoT Communications in 5G and 6G”, filed Oct. 27, 2021,and U.S. Provisional Patent Application Ser. No. 63/313,380, entitled“Short-Form 5G/6G Pulse-Amplitude Demodulation References”, filed Feb.24, 2022, all of which are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

Disclosed are short-form demodulation references and demodulationprocedures for pulse-amplitude modulation, low-complexity devices, andnoise/interference mitigation in a high-density 5G/6G wireless network.

BACKGROUND OF THE INVENTION

A demodulation reference is a message or message portion that exhibitscertain modulation levels of a modulation scheme. Demodulationreferences thereby assist the receiving entity in demodulating asubsequent message. In 5G and 6G, communications may be modulatedaccording to PAM (pulse-amplitude modulation) in which the binary bitsof a message are divided between two parallel signals or “branches”. Thetwo branches (termed I and Q) are amplitude-modulated according to themessage bits, and then summed with a 90-degree phase offset beforetransmitting. The primary demodulation reference is a DMRS (demodulationreference signal) which is configured according to one of a number ofpseudorandom sequences according to a complex formula. However, someuser devices may have difficulty processing such 5G and 6G requirements,or accommodating the bulky DMRS in their reception. In addition, thefluctuating interference background in high-density wirelessenvironments, such as a dense urban area or an automated factoryenvironment, may cause demodulation faults, resulting in missed calls,reduced reliability, and time-consuming retransmissions. What is neededis a demodulation reference configured for use by reduced-capabilitydevices and high-performance users alike, suitable for messaging in bothlow-density and high-density wireless traffic environments.

This Background is provided to introduce a brief context for the Summaryand Detailed Description that follow. This Background is not intended tobe an aid in determining the scope of the claimed subject matter nor beviewed as limiting the claimed subject matter to implementations thatsolve any or all of the disadvantages or problems presented above.

SUMMARY OF THE INVENTION

In a first aspect, there is a method for demodulating a wirelessmessage, the message comprising message elements, each message elementmodulated according to a modulation scheme, the modulation schemecomprising integer Nlevel predetermined amplitude levels, Nlevel greaterthan or equal to two, the method comprising: receiving a demodulationreference comprising integer Nref reference elements, Nref less than orequal to four; extracting, from each reference element, an I-branchsignal having an I-branch amplitude, and a Q-branch signal having aQ-branch amplitude, the I-branch signal phase-shifted relative to theQ-branch signal; determining, based at least in part on the NrefI-branch amplitudes and the Nref Q-branch amplitudes, the Nlevelpredetermined amplitude levels of the modulation scheme; anddemodulating each message element according to the predeterminedamplitude levels.

In another aspect, there is non-transitory computer-readable media in awireless receiver, the media containing instructions that when executedby a computing environment cause a method to be performed, the methodcomprising: receiving a demodulation reference comprising exactly onereference element modulated according to a modulation scheme, themodulation scheme comprising integer Nlevel amplitude levels, theamplitude levels including a minimum positive amplitude level and amaximum positive amplitude level, wherein a predetermined amplituderatio equals the maximum positive amplitude level divided by the minimumpositive amplitude level; extracting, from the reference element, afirst branch signal having a first branch amplitude, and a second branchsignal having a second branch amplitude, the second branch signalphase-shifted relative to the first branch signal; and setting themaximum positive amplitude level equal to the first branch amplitude andthe minimum positive amplitude level equal to the second branchamplitude.

In another aspect, there is a wireless communication device configuredto: receive a demodulation reference modulated according to a modulationscheme, the modulation scheme comprising integer Nlevel predeterminedamplitude levels, the demodulation reference comprising exactly tworeference resource elements, each reference resource element comprisinga first branch signal and a second branch signal phase-shifted relativeto the first branch signal; determine four reference amplitude valuesaccording to the first and second branch signals of the two referenceresource elements, respectively; and determine the Nlevel amplitudelevels according to the four reference amplitude values.

This Summary is provided to introduce a selection of concepts in asimplified form. The concepts are further described in the DetailedDescription section. Elements or steps other than those described inthis Summary are possible, and no element or step is necessarilyrequired. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended foruse as an aid in determining the scope of the claimed subject matter.The claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

These and other embodiments are described in further detail withreference to the figures and accompanying detailed description asprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic showing an exemplary embodiment of a wavemodulated using pulse-amplitude modulation, according to someembodiments.

FIG. 1B is a constellation table showing an exemplary embodiment of apulse-amplitude demodulation scheme based on real and imaginarycomponents, according to some embodiments.

FIG. 1C is a modulation table showing an exemplary embodiment of aclassical modulation scheme based on multiplexed amplitude and phasemodulation, according to some embodiments.

FIG. 1D is a sketch showing an exemplary embodiment of the in-phase andquadrature-phase waves of a pulse-amplitude modulation scheme, accordingto some embodiments.

FIG. 1E is a sketch showing an exemplary embodiment of the branchamplitudes of a pulse-amplitude modulation scheme, according to someembodiments.

FIG. 1F is a sketch showing an exemplary embodiment of the raw signalamplitudes and phases of a modulation scheme, according to someembodiments.

FIG. 2A is a phase chart showing an exemplary embodiment of the rawsignal properties of a pulse-amplitude modulation scheme, according tosome embodiments.

FIG. 2B is a constellation table showing an exemplary embodiment of thestates of 16QAM with pulse-amplitude modulation, according to someembodiments.

FIG. 2C is a phase chart showing an exemplary embodiment of a 4-pointshort-form pulse-amplitude demodulation reference, according to someembodiments.

FIG. 2D is a constellation table showing an exemplary embodiment of a4-point short-form pulse-amplitude demodulation reference specifyingfour states, according to some embodiments.

FIG. 2E is a phase chart showing another exemplary embodiment of a4-point short-form pulse-amplitude demodulation reference, according tosome embodiments.

FIG. 2F is a constellation table showing another exemplary embodiment ofa 4-point short-form pulse-amplitude demodulation reference specifyingfour amplitude levels, according to some embodiments.

FIG. 2G is a phase chart showing an exemplary embodiment of a 4-pointshort-form pulse-amplitude demodulation reference for QPSK, according tosome embodiments.

FIG. 2H is a constellation table showing an exemplary embodiment of a4-point short-form pulse-amplitude demodulation reference for QPSK,according to some embodiments.

FIG. 3A is a sequence chart showing an exemplary embodiment of a processfor demodulating a message using a four-point short-form pulse-amplitudedemodulation reference, according to some embodiments.

FIG. 3B is a flowchart showing an exemplary embodiment of a process fordemodulating a message using a four-point short-form pulse-amplitudedemodulation reference, according to some embodiments.

FIG. 4A is a phase chart showing an exemplary embodiment of a 2-pointshort-form pulse-amplitude demodulation reference, according to someembodiments.

FIG. 4B is a constellation table showing an exemplary embodiment of a2-point short-form pulse-amplitude demodulation reference, according tosome embodiments.

FIG. 4C is a phase chart showing another exemplary embodiment of a2-point short-form pulse-amplitude demodulation reference specifying twoamplitude and phase levels, according to some embodiments.

FIG. 4D is a constellation table showing another exemplary embodiment ofa for a 2-point short-form pulse-amplitude demodulation referencespecifying two amplitude and phase levels, according to someembodiments.

FIG. 4E is a phase chart showing another exemplary embodiment of a2-point short-form pulse-amplitude demodulation reference specifying twoamplitude and phase levels, according to some embodiments.

FIG. 4F is a constellation table showing another exemplary embodiment ofa 2-point short-form pulse-amplitude demodulation reference specifyingtwo amplitude and phase levels, according to some embodiments.

FIG. 4G is a phase chart showing an exemplary embodiment of a 2-pointshort-form pulse-amplitude demodulation reference for QPSK, according tosome embodiments.

FIG. 4H is a constellation table showing an exemplary embodiment of a2-point short-form pulse-amplitude demodulation reference for QPSK,according to some embodiments.

FIG. 5A is a sequence chart showing an exemplary embodiment of a processfor demodulating a message using a two-point short-form pulse-amplitudedemodulation reference, according to some embodiments.

FIG. 5B is a flowchart showing an exemplary embodiment of a process fordemodulating a message using a two-point short-form pulse-amplitudedemodulation reference, according to some embodiments.

FIG. 6A is a phase chart showing an exemplary embodiment of a 1-pointshort-form pulse-amplitude demodulation reference, according to someembodiments.

FIG. 6B is a constellation table showing an exemplary embodiment of a1-point short-form pulse-amplitude demodulation reference, according tosome embodiments.

FIG. 6C is a phase chart showing another exemplary embodiment of a1-point short-form pulse-amplitude demodulation reference, according tosome embodiments.

FIG. 6D is a constellation table showing another exemplary embodiment ofa 1-point short-form pulse-amplitude demodulation reference, accordingto some embodiments.

FIG. 6E is a phase chart showing another exemplary embodiment of a1-point short-form pulse-amplitude demodulation reference, according tosome embodiments.

FIG. 6F is a constellation table showing another exemplary embodiment ofa 1-point short-form pulse-amplitude demodulation reference, accordingto some embodiments.

FIG. 6G is a phase chart showing an exemplary embodiment of a 1-pointshort-form pulse-amplitude demodulation reference for QPSK, according tosome embodiments.

FIG. 6H is a constellation table showing an exemplary embodiment of a1-point short-form pulse-amplitude demodulation reference for QPSK,according to some embodiments.

FIG. 7A is a sequence chart showing an exemplary embodiment of a processfor demodulating a message using a one-point short-form pulse-amplitudedemodulation reference, according to some embodiments.

FIG. 7B is a flowchart showing an exemplary embodiment of a process fordemodulating a message using a one-point short-form pulse-amplitudedemodulation reference, according to some embodiments.

FIG. 8A is a modulation table showing an exemplary embodiment of statesof a pulse-amplitude modulation scheme displayed according to the phaseand amplitude of the raw signal, according to some embodiments.

FIG. 8B is a modulation table showing an exemplary embodiment of afour-point demodulation reference modulated according to apulse-amplitude modulation scheme and displayed according to the phaseand amplitude of the raw signal, according to some embodiments.

FIG. 9 is a flowchart showing an exemplary embodiment of a process forchecking a demodulation reference, which is configured inpulse-amplitude modulation and analyzed according to the phase andamplitude of the raw signal, according to some embodiments.

FIG. 10A is a schematic showing an exemplary embodiment of a resourcegrid with two-point short-form pulse-amplitude demodulation referencesinterspersed within a message, according to some embodiments.

FIG. 10B is a schematic showing an exemplary embodiment of a resourcegrid with one-point short-form pulse-amplitude demodulation referencesinterspersed within two messages, according to some embodiments.

Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

5G and 6G technologies are designed for eMBB (enhanced Mobile Broadbandcommunications), URLLC (ultra reliable low latency communications), andmMTC (massive machine-type communication) generally involving largenumbers of user devices such as vehicles, mobile phones, self-propelledand robotic machines, portable and stationary computers, and many otheradvanced wireless instruments. However, many future IoT (internet ofthings) use cases are expected to involve simple, low-cost,reduced-capability MTC (machine-type communication) wireless devices.For example, a temperature sensor or a door alarm or a timer, amonginnumerable other task-based wireless products, may include a low-costprocessor such as a small microcontroller or an ASIC(application-specific integrated circuit) and may have minimal wirelesscommunication needs. Future automated factories are expected to uselarge numbers of such single-purpose wireless devices in a high-densitycommunication environment. Reduced-capability processors may havedifficulty performing complex 5G/6G procedures, which were developed forhighly competent devices that require high-performance communicationservices. Because both high-performance and reduced-capability devicesshare the same, limited electromagnetic spectrum, it would be tragic ifthe simpler machine-type applications are forced to develop a separatewireless technology, competing with 5G and 6G for bandwidth andlocations. A much more efficient solution is to include, in 5G and 6G, aset of simpler protocols and defaults appropriate for the low-cost,low-demand MTC devices. Experience with 4G has shown that incorporatingsuch flexibility into an already established radio-communicationtechnology is difficult. Therefore, if 5G and 6G are to makeaccommodation for reduced-capability systems in IoT applications,appropriate procedures and options should be incorporated as early inthe development as possible.

A related problem pertains to interference in high-density wirelessenvironments where thousands or millions of devices are in radio rangeof each other, such as an urban center or a highly automatedmanufacturing center. Background interference from the sea ofelectromagnetic signaling may cause frequent modulation distortions ineach message, degrading reliability, causing message faults,interruptions, delays, and missed calls, leading to severely limitednetwork throughput. Moreover, the retransmissions resulting from suchfaults will contribute further to the overall background, making theunderlying problem even worse. Interference is intrinsically bursty andfrequency-rich, that is, fluctuating rapidly in both time and frequency.Demodulation references can mitigate the interference problem byupdating the current amplitude and phase modulation levels to compensatefor the current interference effects, and may thereby assist indemodulating a subsequent message accurately despite interference.Systems and methods disclosed herein (the “systems” and “methods”, alsooccasionally termed “embodiments” or “arrangements”, generally accordingto present principles) can provide urgently needed wirelesscommunication protocols to reduce messaging complexity and delays,facilitate low-complexity demodulation, enable more frequentdemodulation calibration in noisy environments, and provide readilyavailable options to accommodate reduced-capability user devices,according to some embodiments. The motivation behind the presentdisclosure is to provide a demodulation reference option, suitable forboth high-performance and low-cost devices, in sparse rural as well asdense urban/industrial wireless environments.

Disclosed herein are short, low-complexity “PAM” (pulse-amplitudemodulation) demodulation references, configured to provide enhancedmodulation and demodulation in 5G and 6G networks. In PAM, eachmodulated message resource element is prepared by amplitude-modulatingtwo sinusoidal signals separately, and then adding them togetherphase-shifted by 90-degrees. Each of the component signals may be calleda “branch”, such as the “I-branch” and “Q-branch” (I for in-phase, Q forquadrature-phase) or “real and imaginary”, among other terms. Theas-received signal is termed a “raw signal” herein. The raw signal isgenerally equal to the sum of the two branch signals. The raw signal maybe demodulated by separating the branch signals according to phase,measuring the amplitude of each branch signal, and comparing the branchamplitudes to a predetermined set of amplitude levels including all ofthe branch amplitude levels of the modulation scheme. Such a set ofpredetermined amplitudes may be termed a “calibration set” herein. Thepredetermined amplitudes are generally provided by a demodulationreference before the message is transmitted. Pulse-amplitude modulationis in contrast to “classical” amplitude and phase modulation, in whicheach message element is amplitude modulated and separately(orthogonally) phase modulated. Classical modulation and PAM modulationprovide distinct advantages and disadvantages regarding noise mitigationand error correction, as detailed below.

The systems and methods include a receiver configured to demodulate theraw signal in both ways, by (a) measuring the raw signal amplitude andphase, and comparing to a first calibration set that includes thepredetermined raw signal amplitudes and phases of the states of themodulation scheme, and (b) separating the I-branch and Q-branch, andmeasuring each branch amplitude, then comparing those amplitude valuesto a second calibration set containing the predetermined branchamplitudes of the states of the modulation scheme. Although the branchsignals are generally considered to be determined by the raw signalamplitude and phase, and vice-versa, numerous non-ideal effects candistort that association, particularly involving phase shifts. Forexample, the receiver may detect a faulted message element according toa deviation in the raw signal demodulation procedure which the I and Qbranch demodulation procedure may miss, or vice-versa. In addition, thereceiver may reveal an unexpected inconsistency between the twodemodulation results, indicating a deeper error, among other problemsthat can be potentially revealed by one or the other procedure, or acomparison of the two demodulation results.

Terms herein generally follow 3GPP (third generation partnershipproject) standards, but with clarification where needed to resolveambiguities. As used herein, “5G” represents fifth-generation, and “6G”sixth-generation, wireless technology in which a network (or cell or LANLocal Area Network or RAN Radio Access Network or the like) may includea base station (or gNB or generation-node-B or eNB or evolution-node-Bor AP Access Point) in signal communication with a plurality of userdevices (or UE or User Equipment or user nodes or terminals or wirelesstransmit-receive units) and operationally connected to a core network(CN) which handles non-radio tasks, such as administration, and isusually connected to a larger network such as the Internet. Thetime-frequency space is generally configured as a “resource grid”including a number of “resource elements”, each resource element being aspecific unit of time termed a “symbol period”, and a specific frequencyand bandwidth termed a “subcarrier” (or “subchannel” in somereferences). Symbol periods may be termed “OFDM symbols” (OrthogonalFrequency-Division Multiplexing) in references. The time domain may bedivided into ten-millisecond frames, one-millisecond subframes, and somenumber of slots, each slot including 14 symbol periods. The number ofslots per subframe ranges from 1 to 8 depending on the “numerology”selected. The frequency axis is divided into “resource blocks” (alsotermed “resource element groups” or “REG” or “channels” in references)including 12 subcarriers. Each subcarrier is at a slightly differentfrequency. The “numerology” of a resource grid corresponds to thesubcarrier spacing in the frequency domain. Subcarrier spacings of 15,30, 60, 120, and 240 kHz are defined in various numerologies. Eachsubcarrier can be independently modulated to convey message information.Thus a resource element, spanning a single symbol period in time and asingle subcarrier in frequency, is the smallest unit of a message.Standard modulation schemes in 5G and 6G include BPSK (binaryphase-shift keying), QPSK (quad phase-shift keying), 16QAM (quadratureamplitude modulation with 16 modulation states), 64QAM, 256QAM andhigher orders. Most of the examples below relate to QPSK or 16QAM, withstraightforward extension to the other levels of modulation. Forexample, 16QAM modulated according to PAM exhibits two phase levels atzero and 90 degrees (or in practice, for carrier suppression, ±45degrees) and four amplitude levels including two positive and twonegative, thus forming 16 distinct modulation states. Communication in5G and 6G generally takes place on abstract message “channels” (not tobe confused with frequency channels) representing different types ofmessages, embodied as a PDCCH and PUCCH (physical downlink and uplinkcontrol channels) for transmitting control information, PDSCH and PUSCH(physical downlink and uplink shared channels) for transmitting data andother non-control information, PBCH (physical broadcast channel) fortransmitting information to multiple user devices, among other channelsthat may be in use. In addition, one or more random access channels mayinclude multiple random access channels in a single cell. “CRC” (cyclicredundancy code) is an error-checking code. “RNTI” (radio networktemporary identity) is a network-assigned user code. “SNR”(signal-to-noise ratio) and “SINR” (signal-to-interference-and-noiseratio) are used interchangeably unless specifically indicated. “RRC”(radio resource control) is a control-type message from a base stationto a user device.

In addition to the 3GPP terms, the following terms are defined herein.Although in references a modulated resource element of a message may bereferred to as a “symbol”, this may be confused with the same term for atime interval, among other things. Therefore, each modulated resourceelement of a message is referred to as a “modulated message resourceelement”, or more simply as a “message element”, in examples below. A“demodulation reference” is a set of Nref modulated “reference resourceelements” that exhibit levels of a modulation scheme (as opposed toconveying data). Thus integer Nref is the number of reference resourceelements in the demodulation reference. A “calibration set” is one ormore amplitude values (and optionally phase values), which have beendetermined according to a demodulation reference, representing thepredetermined amplitude levels of a modulation scheme. Generally themodulation scheme includes integer Nlevel predetermined amplitudelevels, including the positive and negative values.

“PAM” (pulse-amplitude modulation, not to be confused with signalgeneration by rapid pulsatile energy bursts) is a message modulationtechnology in which bits of a message are allocated to two sinusoidal“branch” signals, which are amplitude-modulated to encode the messagebits, and then summed with a 90-degree phase offset, and transmitted.(In contrast, “classical” amplitude-phase modulation includes amplitudemodulation multiplexed with phase modulation of each message element.) Areceiver can receive a PAM-transmitted raw signal, separate the twobranch signals, and measure their amplitudes. The receiver candemodulate the message elements by separating the two branch signals,measuring their amplitudes, and comparing to a set of predeterminedamplitude levels of the PAM modulation scheme. The branches may betermed the “real” and “imaginary” branches, or the “I and Q” (in-phaseand quadrature-phase) branches, as mentioned. A “constellation table” isa chart showing the I and Q modulation states of a PAM modulationscheme. The “raw signal” is the as-received signal of a message elementor a reference element, prior to separation of the branch signals. Areceiver, upon receiving the raw signal, can separate the two branchesand measure the amplitude of each branch. A “branch amplitude” is theamplitude of an I or Q branch signal, as determined by a receiver. Inthe context of branch amplitudes, a “maximum negative” amplitude is anamplitude with a negative sign and the largest magnitude of themodulation scheme, while the “minimum negative” amplitude is anamplitude with a negative sign and the smallest magnitude. Thus“maximum” and “minimum”, in the context of amplitudes, refer to themagnitudes of the amplitude levels.

The receiver can demodulate a message element by extracting its I and Qbranch signals, measuring their branch amplitudes, and comparing to thepredetermined Nlevel amplitude levels of a calibration set. Thepredetermined modulation levels of the calibration set may beaccumulated from the branch amplitudes of a preceding demodulationreference, plus additional levels calculated from the exhibited branchamplitudes by interpolation, or based on an amplitude ratio and/or otherpredetermined parameters. An “amplitude deviation” of a message elementis the difference between its I or Q branch amplitude and the closestpredetermined amplitude level in the calibration set. Accordingly, the“modulation quality” of a message element is a measure of how close theI and Q branch amplitudes are to the closest predetermined amplitudelevel of the modulation scheme, or equivalently how close the modulationof the message element is to the closest state of the modulation scheme,as indicated by amplitude levels in the calibration set. Thus the“closest state” of the modulation scheme to a particular message elementis the state that has the closest predetermined amplitude levels to theI-branch and Q-branch amplitudes of the message element. Each statecorresponds to a first predetermined amplitude level (closest to themessage element's I-branch amplitude) and a second predeterminedamplitude level (closest to the message element's Q-branch amplitude).The closest state to a particular message element is the state in whichthe difference between the first predetermined amplitude is closest tothe message element's I-branch amplitude and the second predeterminedamplitude is closest to the message element's Q-branch amplitude. Themodulation quality may be calculated by adding those differences inmagnitude, or the square root of the sum of the squares of thedifferences, or other formula relating the deviation of the messageelement's amplitudes from the modulation state's amplitudes.

Each of the I-branch and Q-branch signals may be amplitude modulatedaccording to one of the Nlevel predetermined amplitude levels. Forexample, 16QAM has two predetermined positive amplitude levels, such as+1 and +3 (in some units), and two predetermined negative amplitudelevels, such as −1 and −3. Thus each I or Q branch can then be amplitudemodulated as −3, −1, +1, or +3, thereby representing four possiblebranch amplitude values. Each message element includes two branches (Iand Q), each of which has four branch amplitude possibilities, therebyproviding 4×4=16 total modulation states, as expected for 16QAM. Themodulation scheme may be characterized by an “amplitude ratio” equal tothe maximum branch amplitude level divided by the minimum branchamplitude level of the modulation scheme. The same amplitude ratio alsoapplies to the branch amplitudes and the raw signal amplitudes. In16QAM, the amplitude ratio is 3. This provides that the branchamplitudes are uniformly spaced, that is, the branch amplitude levelsare separated by 2 units in the current example (−3, −1, +1, +3).

For 64QAM, there are 8 branch amplitude levels (−7, −5, −3, −1, +1, +3,+5, +7 in some units) and hence the amplitude ratio is 7 (maximumpositive level divided by minimum positive level, or 7 divided by 1). In256QAM, the amplitude ratio is 15. In general, the amplitude ratio inPAM equals the square root of the number of modulation states, minusone. The amplitude of the raw signal itself is determined by thetrigonometric sum of the two branch signals, accounting for their phasedifference. For example, the raw signal amplitude levels for 16QAM are,to sufficient accuracy, 1.414, 3.165, and 4.243 in the same units as thebranch amplitudes mentioned above. These three amplitude levelscorrespond to the sum of I and Q branch signals at the minimum (+1)branch amplitude, the sum of a minimum and a maximum (+1 and +3), andthe sum of two maximum branch amplitude signals (+3), respectively.

“Low-complexity” refers to devices and procedures necessary for wirelesscommunication, exclusive of devices and procedures that providehigh-performance communication. 5G/6G specifications include manyprocedures and requirements that greatly exceed those necessary forwireless communication, in order to provide high-performancecommunications at low latency and high reliability for users that demandit. Compared to scheduled and managed 5G/6G messaging, low-complexityprocedures generally require less computation and less signalprocessing. For example, low-complexity procedures may be tailored tominimize the number of separate operations required of a device per unitof time. 5G and 6G specifications include a very wide range of optionsand contingencies and versions and formats and types and modes for manyoperations, to achieve maximum flexibility. A low-complexityspecification may include defaults for each operation, and thosedefaults may be the simplest choices, or at least simpler than standard5G and 6G procedures. “Simpler” procedures generally require fewercomputation steps and/or smaller memory spaces than correspondingprocedures in standard 5G/6G. Computation steps may be measured infloating-point calculations, for example.

“Reduced-capability” refers to wireless devices that cannot comply with5G or 6G protocols, absent the systems and methods disclosed herein. Forexample, regular 5G and 6G user devices are required to receive a 5 MHzbandwidth in order to receive system information messages. Regular userdevices are required to perform high-speed signal processing such asdigitizing the received waveform, applying digital filtering or Fouriertransforming an incoming waveform, phase-dependent integrating atseveral GHz frequency, and separating closely-spaced subcarriers. Areduced-capability device, on the other hand, may not need the highperformance gained by such procedures, and may be incapable ofperforming them. A reduced-capability device may be able to receive anarrow-band wireless signal, demodulate the message, and interpret thecontent without further processing.

“High-density” wireless communication refers to cells where the numberof active transmitters per unit area challenges the ability of thenetwork to manage the traffic without degraded service. For example, ina built-up urban environment, a city block of 100×200 m² with 10-storeyapartment buildings, 100 m² per apartment at double occupancy, andconservatively assuming 5 wireless devices per person (phones, watches,fitness bands, and whatnot) plus 10 wireless devices per apartment(computers, smart appliances, doorbell cameras, temperature sensors, dogcollars, etc.), almost all of them being always-on devices, the activedevice density is then 40,000 devices per city block or about 2 devicesper square meter. The road space between blocks scarcely reduces thisload because it is typically filled with heavily-linked vehicles,traffic signals, wireless advertising signs, smart trash cans, andwhatever future inventors can devise. Basic physics says with confidencethat the electromagnetic background will be significant and fluctuating.

For economic reasons as well as commercial feasibility, future IoTapplication developers will demand ways to transmit messages usingbandwidths and protocols appropriate to the simpler devices. It isimportant to provide such low-complexity options early in the 6Groll-out, while such flexibility can still be incorporated in the systemdesign. Accordingly, the systems and methods disclosed herein include“short-form pulse-amplitude demodulation references”, or “SF-PAdemodulation references”. These are low-complexity PAM-compatibledemodulation references suitable for reduced-capability user devices aswell as high-performance devices. In some embodiments, thelow-complexity short-form pulse-amplitude demodulation references may beshort messages, such as 1 or 2 or 3 or 4 resource elements in length,and thus may be termed “short-form” due to their reduced size relativeto the demodulation references of prior art. They are PAM-compatible inthat each message element of a message can be demodulated by measuringits I and Q amplitude values and comparing to the Nlevel predeterminedamplitude levels in a calibration set, obtained from a precedingshort-form pulse-amplitude demodulation reference.

In some embodiments, a short-form pulse-amplitude demodulation referencemay explicitly show just a subset of the Nlevel branch amplitude levelsof the pulse-amplitude modulation scheme, yet may provide sufficientinformation that a receiver can calculate the remaining modulationlevels and thereby demodulate a subsequent message. In particular,assuming the same noise and interference apply to the demodulationreference, the subsequent message demodulation may largely cancel thenoise and interference effects. If a base station supports alow-complexity channel to accommodate the lowered communication needs ofsimpler wireless devices, the short-form pulse-amplitude demodulationreferences disclosed herein may be readily incorporated as the defaultdemodulation reference for communications in that channel. In addition,the high-performance scheduled and managed channels of 5G/6G maybeneficially employ short-form pulse-amplitude demodulation referencesfor reduced latency, higher throughput, and improved interferencerejection in noisy environments, due to the reduced size and complexityof the short-form pulse-amplitude demodulation references. In addition,improved SNR may be obtained by analyzing each message element'smodulation using both PAM and classical amplitude-phase technologies, asdescribed below.

Numerous formats of the short-form PAM demodulation reference areenvisioned and disclosed. Due to the many possible versions listed andenvisioned, it would be helpful for a wireless standards committee todeclare one of the short-form pulse-amplitude demodulation versions tobe a default standard.

Turning now to the figures, in a first example, the branches of aPAM-modulated message element are compared to a classicalamplitude-phase modulated message element.

FIG. 1A is a schematic showing an exemplary embodiment of a wavemodulated using pulse-amplitude modulation, according to someembodiments. As depicted in this non-limiting example, wavesrepresenting modulated signals are shown as in an oscilloscope display,with voltage vertical and time horizontal. A first wave 101 representsthe real or “I” branch, phased at zero degrees with a particularamplitude as shown. The second wave 102 is the imaginary or “Q” branch,phased at 90 degrees, and has a negative amplitude in this case. Thethird wave 103 (“raw signal”) is the sum of the first and second waves101 and 102, representing the transmitted or received waveform. Areceiver, upon detecting the raw signal wave 103, can demodulate it bymeasuring the zero-degree I amplitude, indicated as a square 104 at zerodegrees, and the 90-degree Q amplitude 105. These values 104, 105 arethe “branch amplitudes”. In the absence of noise or interference, the Qsignal is zero at the instant (or phase) when the I branch is measured,and the I signal is zero when the Q branch is measured. Hence eachphased measurement detects only one of the branches at at a time, inprinciple. The receiver can then determine the modulation stateaccording to the signs and ratios of those branch amplitude values. Forexample, a particular modulation scheme may have four amplitude values,termed a maximum positive amplitude, the minimum positive amplitude, theminimum negative amplitude, and the maximum negative amplitude. Hencethere are four possible values for the I branch, and another four forthe Q branch. The receiver generally assumes that the two branches havethe same predetermined amplitude levels, absent phase-dependentinterference. The raw wave 103 is the sum of an I signal and a Q signal,and each can have four values. Hence, there are 16 possible states, andthe modulation scheme is 16QAM.

In some embodiments, the receiver can measure the amplitude and phase ofthe as-received raw signal 103 in addition to the I and Q branchamplitudes. The amplitude of the raw signal 103 is shown as 106, and thephase (measured to the positive peak) is shown as 107. Although the rawsignal amplitude and phase are deterministically related to the I and Qbranch amplitudes, the receiver can acquire additional information aboutnoise and interference effects, as well as timing errors, by measuringthe branch amplitudes and the raw signal properties, and comparing themto a calibration set or to the branch amplitudes, seekinginconsistencies or low modulation quality. In addition, depending on themeasurement uncertainties, the receiver can detect distortions in thephase and amplitude of the as-received wave more readily than in thebranch amplitudes, or vice-versa. The receiver can compare the rawsignal phase and amplitude data with the branch amplitude data to revealotherwise undetected or subtle noise and interference effects, and maythereby identify which message elements are at fault in a corruptedmessage. After identifying one or more “suspicious” or inconsistent orpoor-modulation message elements, the receiver may attempt to correctthe message by altering the faulted message elements. If the number ofsuspicious message elements is small, the alteration search may takeless time than requesting a retransmission.

FIG. 1B is a “constellation chart” showing an exemplary embodiment of ademodulation scheme based on real and imaginary components, according tosome embodiments. As depicted in this non-limiting example, aconstellation chart is an array showing all of the PAM modulationstates, plotted with the amplitude of the I branch horizontally and theamplitude of the Q branch vertically. Thus the constellation chart showsall valid combinations of the I and Q branch amplitudes in themodulation scheme. The central cross shape on the chart divides thepositive and negative amplitude values. Each modulation state is shownas a square 110 indicating the amplitudes of the I and Q branches. Inthis case, the modulation scheme is 16QAM with 16 states. One of themodulation states is stippled 111, representing a maximally positive Iamplitude and a maximally negative Q amplitude. Hence, the state 111corresponds to the raw signal wave 103 of the previous figure.

FIG. 1C is a “modulation table” showing an exemplary embodiment of ademodulation scheme based on classical amplitude and phase modulation,according to some embodiments. As depicted in this non-limiting example,the modulation table shows all of the valid modulation states of themodulation scheme, plotted with the raw signal phase horizontally andthe raw signal amplitude vertically. All amplitude and phase levels arepositive. There are four amplitude levels and four phase levels in thiscase, corresponding to 16QAM. Each valid state of the modulation schemeis shown as a circle 120. A particular state 121 has the maximum phaseand the maximum amplitude of the raw signal wave. Hence the state 121corresponds to the raw signal wave 103 of FIG. 1A and also to theconstellation state 111 of FIG. 1B.

FIG. 1D is a chart showing an exemplary embodiment of I and Q branchwaveforms of a PAM modulation scheme, according to some embodiments. Asdepicted in this non-limiting example, the wave shapes are shown versusphase (or equivalently, versus time) with four exemplary I waves at thetop and four exemplary Q waves at the bottom of the chart. Each wave canhave a maximum or minimum branch amplitude, and can have positive ornegative sign, and can be phased at zero or 90 degrees (as the I or Qbranches), hence forming eight different waves as shown. The I branchwaves 131-134 and the Q-branch waves 135-138 form the components of themodulation scheme. Wave 131 has the maximum branch amplitude and apositive sign, while wave 132 has the minimum branch amplitude and apositive sign. Waves 133 and 134 have a negative sign (shown dashed) andhave the minimum and maximum branch amplitudes, respectively. Likewisewaves 135-138 are on the Q branch with 135 and 136 having positive maxand min branch amplitudes, while 137 and 138 have the negative min andmax branch amplitudes.

The modulation state is determined by the magnitude of the amplitude andthe sign of the amplitude, measured at zero degrees for I and at 90degrees for Q. The modulation scheme generally uses a small numberNlevel of predetermined branch amplitude levels. In this case, Nlevelequals four predetermined amplitude levels. The transmitter encodes themessage data by constructing the states of the modulation scheme, bymultiplexing the I and Q branches using only those predeterminedamplitude levels. QPSK has two predetermined amplitude levels, therebygenerating four states by combining the I and Q branches. 16QAM has fourI and four Q branch amplitudes which, when multiplexed, provides 16states. Higher order modulation schemes have additional levels. Thepredetermined amplitude levels are generally selected so that the branchwaves are equally spaced, as suggested in the figure. For example, for16QAM, the maximum may be 3 times the minimum amplitude, so that thespacing between the max and min positive waves equals the spacingbetween the min positive and min negative waves, which is equal to thespacing between the negative min and max waves, as shown. Forhigher-order modulation schemes, the branch amplitudes may be selectedso as to preserve the uniform spacing.

FIG. 1E is a sketch showing an exemplary embodiment of the branchamplitudes of a pulse-amplitude modulation scheme, according to someembodiments. As depicted in this non-limiting example, the four positiveand negative branch amplitudes 141 of a PAM modulation scheme for 16QAMare shown for the zero-noise case on the left, and with additive noiseon the right. The four predetermined branch amplitudes 141 include themaximum positive amplitude, the minimum positive amplitude, the minimumnegative amplitude, and the maximum negative amplitude levels, equallyspaced, which correspond to the waves 131, 132, 133, 134 of the previousfigure. The I and Q branches are generally assumed to have the samebranch amplitudes, absent phase-dependent interference.

Also shown are the branch amplitudes with additive noise 142. The noiseshift is shown as 143, and is assumed the same for all branchamplitudes, that is, additive noise. By measuring the branch amplitudesof a demodulation reference, and then using those values to demodulate asubsequent message, the receiver can mitigate additive noise andinterference, in some embodiments.

FIG. 1F is a sketch showing an exemplary embodiment of the raw signalamplitudes and phases of a modulation scheme, according to someembodiments. As depicted in this non-limiting example, the amplitudes151 of the raw signal (as-received, prior to I/Q branch separation) areshown, transmitted in PAM modulation but now analyzed for the rawas-received signal amplitudes and phases. There are only three rawamplitudes 141, corresponding to the maximum positive I branch summedwith the maximum positive Q branch, the minimum positive I branch summedwith the minimum positive Q branch, and one of the maximum positivebranches summed with the other minimum Q branch. Since the raw signalamplitudes are measured in magnitude, there are no negative levels.Instead, there are various raw signal phases 153. For clarity, only fourphases are graphed, representing the four maximum-maximum combinations.The other raw-signal phases are discussed in the next figure.

Also shown, connected by dashed lines, are the raw amplitude levelsshifted by additive noise 152, and the raw phases shifted by noise 154.In some cases, the raw signal properties contain the same information asthe branch signal properties, and the message may be demodulated using acalibration set derived using either method. In many other cases,however, the two methods differ in sensitivity for various reasons. Forexample, the raw signal exposes phase-shift distortions, which are onlyindirectly reflected in the PAM branch amplitudes. In addition, eachphase or amplitude measurement is subject to measurement uncertainties,which can be quite different for amplitude and phase measurements.Moreover, the branch separation is not perfect. These limitations becomemore severe at high frequencies due to short integration times and highphase noise, and become especially critical at high modulation ordersdue to the closely-spaced amplitude levels.

Therefore, the systems and methods include the receiver analyzing eachreceived demodulation reference and message element using bothprocedures, the I and Q branch amplitude measurements of PAM, and theraw signal amplitude and phase measurements. The systems and methodsfurther include the receiver comparing those analysis results to revealfaulted message elements.

The following examples disclose a four-point short-form pulse-amplitudedemodulation reference, with a length of four reference elements,exhibiting the maximum and minimum amplitude levels of the modulationscheme.

FIG. 2A is a phase chart showing an exemplary embodiment of the rawsignal properties of a pulse-amplitude modulation scheme, according tosome embodiments. As depicted in this non-limiting example, a phasechart is a schematic representation of the states of a modulationscheme, in a polar coordinate system in which the phase of theas-received (raw signal) wave is shown azimuthally, and the amplitude ofthe as-received wave is plotted radially. The large circles 201, 202,203 represent the amplitude levels of the raw signal wave, and thestates of the modulation scheme are shown as points such as 204, 205,206. Thus the amplitude of a particular state 207 is indicated by theradius 208 and the phase angle 209. The horizontal axis represents zerodegrees, or unmodulated carrier, which is generally not used for rawsignal modulation. The modulation scheme is 16QAM in this case, withpulse-amplitude modulation.

The points shown in the phase chart correspond to the various branchwaves shown in FIG. 1D. The dark-stippled points 205, at the smallestradius 203, are generated by the minimum-amplitude branch waves inpositive or negative, specifically the 132 or 133 wave summed with the136 or 137 wave. This generates the four states 205. The white points204 are generated by summing the maximum-amplitude waves 131 or 134 with135 or 138. The light-stippled points 205 are various combinations ofone maximum-amplitude branch wave with one minimum-amplitude branchwave, specifically one of 131, 134, 135, 138 added to one of 132, 133,136, 137.

These combinations result in 16 states as shown. The receiver canidentify each received state in two ways: (a) by separating the I-branchand Q-branch signals, measuring their branch amplitudes, and comparingto a first calibration set that includes the predetermined branchamplitude levels, or (b) by measuring the amplitude and phase of theas-received raw signal and comparing to a second calibration set thatincludes those raw signal amplitude levels and phase levels. The twodemodulation procedures have different sensitivities to noise andinterference, because noise and interference can distort the amplitudeand phase of each wave component separately. For example, PAM does notmeasure phase directly, while classical amplitude-phase modulation does.In some embodiments, the receiver may perform both demodulationprocedures, by measuring the raw signal amplitude and phase, thenseparating the I and Q branches and measuring their branch amplitudes.Although in ideal circumstances, the raw signal properties are uniquelydetermined by the branch signals, and vice-versa, the two procedureshave different sensitivities to amplitude-shifting and phase-shiftingnoise or interference. Therefore some distortions may be more readilymitigated with one procedure, while other distortions may be properlytreated with the other procedure, and some may be best revealed (andpossibly mitigated) by comparing the two procedures for each messageelement. The receiver can thereby demodulate message elements moreaccurately, and can identify message elements that are faulted morereadily, using both demodulation procedures, according to someembodiments.

FIG. 2B is a constellation table showing an exemplary embodiment of thestates of 16QAM with pulse-amplitude modulation, according to someembodiments. Each state is shown as a square representing a particularcombination of the positive and negative, maximum and minimum, I and Qwaves. For example, the real (I) axis represents states generated bymultiplexing the positive maximum I-branch amplitude (+max), thepositive minimum I-branch amplitude (+min), the negative minimum andmaximum amplitudes (−min, −max) as labeled. The vertical imaginary axisis labeled similarly, for the Q-branch component. Thus, for example, thestate 216 is generated by multiplexing the maximum positive I-branchwave with the maximum negative Q-branch wave.

The shading corresponds to the points in the previous figure. The whitesquares such as 216 are generated by multiplexing the maximum I and Qamplitudes (positive and negative combinations), which correspond to thewhite points 206 in the previous figure. The dark-stipple squares suchas 215 are generated by the minimum I and Q amplitudes (positive andnegative combinations), corresponding to the dark-stipple points 205.The medium-stipple squares such as 214 are generated by variouscombinations of the maximum and minimum positive and negative I and Qwaves, corresponding to the medium-stipple points 204. Thus the twofigures show the same states, but with emphasis on the raw signalproperties in FIG. 2A, and focusing on the I and Q branch amplitudes inFIG. 2B.

FIG. 2C is a phase chart showing an exemplary embodiment of a 4-pointshort-form pulse-amplitude demodulation reference, according to someembodiments. As depicted in this non-limiting example, a 16QAMmodulation scheme with PAM includes three predetermined raw signalamplitudes 221, 222, and 223. The four-point demodulation referenceincludes four resource elements, labeled 224, 225, 226, 227. In thiscase, the four-point demodulation reference explicitly exhibits allthree raw signal amplitude levels and all four raw signal phasequadrants, thereby assisting the receiver in constructing a classicalamplitude-phase calibration set including the raw signal amplitudes andphases of the as-received signal. In addition, the receiver can separatethe I and Q branches, measure their amplitudes, and thereby fill in thepredetermined branch amplitude levels in a second calibration set. Afterfilling in the various amplitude and phase levels of the two calibrationsets, the receiver can then demodulate each message element of asubsequent message by comparing the raw signal amplitude and phase tothe first calibration set, or the branch amplitudes to the secondcalibration set.

In the depicted case, a first point 224 corresponds to the maximumpositive I-branch amplitude multiplexed with the maximum positiveQ-branch amplitude, thereby generating the maximum raw signal amplitude,and a raw signal phase of 45 degrees. The demodulation reference alsoincludes another point 226 generated by the minimum negative I-branchand Q-branch amplitudes, thus generating the minimum raw signalamplitude and a phase of 225 degrees. To fill in the calibration set,the receiver can compare the raw signal maximum and minimum amplitudesas exhibited by points 224 and 226, calculate the intermediate rawsignal amplitude trigonometrically (that is, with a 90-degreephase-shift), and thereby demodulate the message elements whilemitigating additive noise. Specifically, point 224 exhibits the largestraw signal amplitude plus noise, and point 226 exhibits the smallest rawsignal amplitude plus noise. In addition, if the modulation order ishigher, such as 64QAM or 256QAM, the receiver can calculate the rawsignal amplitudes of the intermediate levels from the observedamplitudes by interpolation.

The two other states of the demodulation reference, point 227 and 225,represent combinations of one of the maximum branch amplitudes with oneof the minimum branch amplitudes, in various plus and minuscombinations. The receiver can use those values to further refine thecalibration set levels. For example, the receiver can measure theamplitudes of the raw signals of points 225 and 227, optionally averagethose measurements for improved resolution, and thereby determine theintermediate amplitude level of the modulation scheme. Alternatively,the receiver can separate the I and Q branches for points 225 and 227,measure the I and Q branch amplitudes for them (which must be equal toeither the maximum or minimum branch amplitudes in this case), andthereby refine the maximum and minimum branch amplitude values in thecalibration set by averaging. Alternatively, the receiver can use themixed points 225 and 227 to quantify non-additive noise andinterference, by comparing the amplitude and phase values of points 225and 227 with those of points 224 and 226. In this way, the receiver canin some cases reveal phase-dependent interference or non-linearnon-additive effects. In addition, the receiver may detect faults thatoccur in the demodulation reference itself, by checking the consistencyof the amplitude and phase levels as deduced from the maximum andminimum points 224 and 226, versus the min-plus-max points 225 and 227.If a receiver determines that the four points are not mutuallyconsistent, given the 16QAM modulation scheme, the receiver can tryseveral things. First, the receiver can adjust the branch amplitudelevels in the calibration set using a best-fit compromise, or thereceiver can select a particular misfit point and ignore it, of thereceiver can reject the demodulation reference entirely and attempt todemodulate the message using an earlier (and possibly “stale”)demodulation reference, or the receiver can reject the message and itsassociated demodulation reference and request a retransmission, amongother options depending on network rules.

FIG. 2D is a constellation table showing an exemplary embodiment of a4-point short-form pulse-amplitude demodulation reference specifyingfour states, according to some embodiments. As depicted in thisnon-limiting example, the real and imaginary components of fourreference elements of the demodulation reference include state 234 withthe maximum positive I and Q branch amplitudes, state 236 with theminimum negative I and Q branch amplitudes, state 235 and 237 each withone maximum and one minimum I and Q branch combined. The stippled states234-237 thus correspond to the points 224-227 of the previous figure.The two FIGS. 2C and 2D show the same information in different forms,with FIG. 2C explicitly showing the raw-signal amplitude and phaseproperties, and FIG. 2D showing the I and Q branches of PAM for the samedemodulation reference.

FIG. 2E is a phase chart showing another exemplary embodiment of a4-point short-form pulse-amplitude demodulation reference, according tosome embodiments. As depicted in this non-limiting example, the phaseand amplitude of each resource element's raw signal, of a 4-pointdemodulation reference, include point 244 with the maximum raw signalamplitude and a raw signal phase of 45 degrees. The demodulationreference also includes point 246 having the maximum raw signalamplitude, and a phase of 225 degrees. Also shown are points 245 and 247with the minimum raw signal amplitude, and phases of 235 and 315degrees. Although none of the demodulation elements exhibits the middleamplitude, this can be calculated from the other two amplitudes bytrigonometrically adding the maximum and minimum amplitudes, asdescribed above.

FIG. 2F is a constellation table showing another exemplary embodiment ofa 4-point short-form pulse-amplitude demodulation reference specifyingfour amplitude levels, according to some embodiments. As depicted inthis non-limiting example, the states of 16QAM with PAM modulation areshown versus the I and Q branch amplitudes including positive andnegative values. The four stippled states correspond to the points ofthe previous figure. State 254 is generated by the maximum I and Qpositive amplitudes, corresponding to point 244. State 256 is generatedby the maximum negative I and Q amplitudes, as point 246. States 255 and257 are generated by the minimum I and Q amplitudes, in this case onebeing positive and the other negative, thereby corresponding to points245 and 247.

An advantage of providing, in the demodulation reference, two oppositemaximum-amplitude states, such as 254 and 256, may be that the receivercan readily calculate the other amplitude levels of the modulationscheme by interpolation. In the present example, no such interpolationis necessary because the other two states, 255 and 257, exhibit theminimum branch amplitudes, thereby enabling the complete calibration setto be filled in, based on the exhibited amplitude values alone. If themodulation scheme were, say, 256QAM, the receiver can calculate theintermediate amplitude levels by interpolating between the two maximalstates 254 and 256 using known amplitude ratios. Alternatively, and evenbetter, the receiver can interpolate between the maximum branchamplitude (as determined by 254 and 254), and the minimum branchamplitude (as determined by 255 and 257). In either case, the receivercan readily calculate the calibration set from the four-pointdemodulation reference.

FIG. 2G is a phase chart showing an exemplary embodiment of a 4-pointshort-form pulse-amplitude demodulation reference for QPSK, according tosome embodiments. As depicted in this non-limiting example, the fourstates of QPSK can be described according to the positive and negative Iand Q signals, all at a single branch amplitude and therefore a singleraw signal amplitude 261. The four raw signal points are 264, 265, 266,and 267, separated by 90 degrees, with a 45-degree carrier-suppressionoffset, on a single raw signal amplitude.

FIG. 2H is a constellation table showing an exemplary embodiment of a4-point short-form pulse-amplitude demodulation reference for QPSK,according to some embodiments. The four states 274, 275, 276, 277 areformed by multiplexing positive and negative I and Q branch signals at aconstant branch amplitude. For example, state 277 is formed from thepositive I wave plus the negative Q wave, both at the same branchamplitude. Thus the states 274, 275, 276, and 277 correspond to thepoints 264, 265, 266, 267 of the previous figure.

An advantage of providing a four-point pulse-amplitude short-formdemodulation reference may be that the I and Q branch amplitude valuesprovided in the demodulation reference may be used to demodulate themessage elements. Another advantage may be that the provided amplitudevalues can explicitly exhibit all of the modulation scheme amplitude andphase levels directly (as in 16QAM), or can be interpolated to calculateall of the unexhibited amplitude and phase levels (as in 256QAM).Another advantage may be that intractable interference can be detectedby inconsistencies between the raw signal phase and amplitude, versusthe I and Q branch amplitudes. For example, the message element may befaulted if the two methods indicate different modulation states. Anotheradvantage may be that the amplitude levels of the modulation scheme maybe determined by interpolating between maximum and minimum branchamplitudes, which are exhibited in the short-form pulse-amplitudedemodulation reference. Another advantage may be that the four-pointshort-form demodulation reference is short, only four referenceelements, and thus may be appended or prepended to other messages, orinterspersed within longer messages, to provide frequent updates of thespecific modulation levels used in an accompanying message, includingeffects of interference. Alternatively, the short-form demodulationreference may be supplied separately from a message, such asperiodically, such as in the first four subcarriers of the first uplinkor downlink symbol period of each slot, or the first four symbol periodsof a single subcarrier in each slot, for example. Another advantage maybe that the four-point short-form demodulation reference may include themaximum and minimum branch amplitude levels of the modulation scheme, inwhich case there may be no need to extrapolate amplitude values beyondthose explicitly exhibited in the short-form demodulation reference,thereby minimizing calculation errors. Another advantage may be thatdistortions, in amplitude or phase or both, due to noise orinterference, may be present in the amplitude and phase values of thereference elements, and therefore those distortions may be canceled whenthe demodulation reference values are then used to demodulate asubsequent message.

Another advantage may be that the procedures of FIG. 2A-2H may beimplemented as a software (or firmware) update, without requiring newhardware development, and therefore may be implemented at low cost,according to some embodiments. The procedures of FIG. 2A-2H may beimplemented as a system or apparatus, a method, or instructions innon-transient computer-readable media for causing a computingenvironment, such as a user device, a base station, or other signallycoupled component of a wireless network, to implement the procedure.Another advantage may be that the depicted low-complexity procedures maybe compatible with devices that may have difficulty complying withprior-art registration procedures. Other advantages may be apparent toone of ordinary skill in the art, given this teaching. The advantageslisted in this paragraph are also true for other lists of advantagespresented for other embodiments described below.

FIG. 3A is a sequence chart showing an exemplary embodiment of alow-complexity procedure for demodulating a message using a short-formpulse-amplitude demodulation reference, according to some embodiments.Actions and events of a receiver are shown on the first line, thenactions or events of a processor connected to the receiver on the secondline, and a result or processor output is shown on the last line. Insequence charts, messages are usually shown time-spanning for clarity,but the messages may be frequency-spanning as well. Arrows show timingor information flow. As depicted in this non-limiting example, thedemodulation reference is a four-point short-form pulse-amplitudedemodulation reference 301, followed by an optional gap 306, and amessage 302 which is to be demodulated, with little marks demarking eachof the message elements. The gap 306 may be one symbol period or more,and may include zero transmission, or transmission with an amplitudebelow the lowest amplitude level of the modulation scheme, orunmodulated carrier (at the subcarrier frequency), or othercharacteristic signal not resembling the data. The gap 306 may bepositioned between the demodulation reference 301 and the message,thereby indicating the end of the demodulation reference 301 and thestarting point of the message 302, which may be helpful to the receiver.The processor may analyze the reference elements of the demodulationreference 301 and may thereby determine the amplitude and phase of theraw signal, and/or the I and Q branch amplitudes, and thereby fill inthe demodulation levels in the calibration set 303. If necessary, theprocessor may interpolate or otherwise calculate additional levels ofthe modulation scheme based on those exhibited in the demodulationreference 301.

Then, the processor may analyze each resource element of the message302, by comparing the I and Q branch amplitudes of each message element302 to the calibration set 303, or comparing the raw signal amplitudeand phase of each message element 302 to the calibration set 303, orboth. Hence the receiver can determine the modulation state of eachmessage element 304 according to the closest match between theamplitudes of the message element and the predetermined amplitude levelsof the calibration set.

The predetermined modulation levels in the calibration set may berepresented numerically. For example, each amplitude (and/or phase)level in the calibration set 303 may be assigned a binary code. In 16QAMwith pulse-amplitude modulation, there are four branch amplitude levels,so the code may be a two-bit binary code, such as 11 for the maximalnegative amplitude level, 10 for the minimal negative level, 00 for theminimal positive level, and 01 for the maximal positive level. In someembodiments, the I branch and Q branch share the same set of four branchamplitude levels, while in other embodiments, separate amplitude levelsare determined for the I and Q branches. In some embodiments, themodulation state of each message element 304 may be represented by a4-bit code indicating which branch amplitude levels in the calibrationset most closely match the branch amplitude values in the messageelement. The 4-bit code may show the I-branch amplitude code, followedby the Q-branch amplitude code, for each message element. For example, amessage element modulated with the maximally negative amplitude level inthe I branch and the maximally positive level in the Q branch would be1101. The message 302 can then be represented by a series 305 of binarybits containing the message information.

The bit-level representation generally depends on the modulation scheme.BPSK represents one bit per message element, QPSK has 2 bits per messageelement, 16QAM has 4 bits per message element, 64QAM requires 6 bits permessage element, and 256QAM would need 8 bits per message element.Assuming the I and Q branches share the same branch amplitude levels,QPSK has only one branch amplitude level, which may be positive ornegative in each branch of each message element. 16QAM has fourpredetermined branch amplitude levels, 64QAM has eight, and 256QAM has16 branch amplitude levels. In some embodiments, the same predeterminedbranch amplitude levels may be assumed in the calibration set, for bothI and Q branches. However, for more complex noise and interferencemitigation, the receiver can determine the predetermined I-branchamplitude levels separately from the Q-branch amplitude levels, based onthe values exhibited in the four-point pulse-amplitude demodulationreference. As a valuable consistency check, the receiver can alsodetermine the amplitude and phase levels of the raw signal, anddetermine whether the modulation state indicated by the raw signalparameters matches that implied by the PAM branch-amplitude levels.

FIG. 3B is a flowchart showing an exemplary embodiment of alow-complexity procedure for using a short-form pulse-amplitudedemodulation reference, according to some embodiments. As depicted inthis non-limiting example, at 350 a receiving entity receives ademodulation reference with four resource elements and, at 351,separately measures the amplitude values of the I and Q branches foreach of its four reference elements. At 352, the receiver determines themaximum and minimum, positive and negative, branch amplitudes, forexample by averaging the various redundant amplitude measurements of themaximum value in the four reference elements, and likewise for theminimum amplitude values. At 353, the receiver determines whether themodulation is higher than 16QAM (according to system information or anRRC message or otherwise). If the modulation is higher than 16QAM, suchas 64QAM or 256QAM, then at 354 the receiver calculates the remainingbranch amplitude levels from those explicitly exhibited in theshort-form demodulation reference elements, by interpolating between themaximum and minimum amplitude values or by extrapolating from theexhibited values, for example. At 355, the branch amplitude values fromthe short-form demodulation reference elements and, if applicable, fromthe calculations, are accumulated as a calibration set which includesall of the predetermined branch amplitude levels of the modulationscheme. In addition, or alternatively, the raw signal parameters (fouramplitudes and four phases for the case of 16QAM) may be accumulated ina second calibration set, and used for raw signal consistency checks,fault identification, and other uses.

At 356 (if not sooner), the message to be demodulated is received. At357, each message element is compared to the branch amplitudes in thecalibration set. The I and Q branch amplitude values of each messageelement are thereby identified according to the closest predeterminedamplitude levels in the calibration set, and each message element isthereby demodulated. Optionally, the receiver may also demodulate themessage element according to the raw signal amplitude and phase using asecond calibration set, and check for errors. At 358, a binaryrepresentation of the message is prepared by concatenating the numbersassociated with each branch amplitude level of each message element, andis done at 359.

An advantage of providing a four-point short-form demodulation referencemay be that it is short, just four reference elements. Another advantagemay be that four modulation states can be explicitly provided, therebyenabling direct demodulation of QPSK or 16QAM without interpolation orextrapolation, in some embodiments. Another advantage may be that highermodulation schemes such as 64QAM or 256QAM may be demodulated, usinginterpolation or extrapolation to derive the remaining levels from theexplicitly provided levels. Another advantage may be that thedemodulation reference values may include any effects of noise andinterference, so that those distortions may be canceled when thereceived reference values are used to demodulate a subsequent message.Another advantage may be that the demodulation reference can includemultiple determinations of the same parameters, such as the maximumand/or minimum branch amplitude values, and thereby obtain a moreprecise determination by averaging.

The systems and methods further include a two-point short-formpulse-amplitude demodulation reference with a length of two referenceelements, as in the following examples.

FIG. 4A is a phase chart showing an exemplary embodiment of a shortlow-complexity demodulation reference such as a two-point short-formdemodulation reference for PAM modulation, according to someembodiments. As depicted in this non-limiting example, the short-formdemodulation reference includes two points representing two referenceelements with particular modulations. In this case, the modulationscheme is 16QAM and the type is PAM, but the interpretation and graphpertain to classical amplitude and phase measurements of the raw signal.The raw signal amplitude levels are indicated as circles 401. Thedemodulation reference includes a first reference element 402 modulatedwith the maximum raw signal amplitude, and a phase of 135 degrees. Thiscorresponds to the maximum negative I-branch amplitude and the maximumpositive Q-branch amplitude in PAM. The demodulation reference alsoincludes a second reference element 403 exhibiting the smallest rawsignal amplitude with a phase of 315 degrees, which corresponds to theminimum positive I-branch amplitude and the minimum negative Q-branchamplitude. The short-form demodulation reference thereby exhibits themaximum and minimum branch amplitude levels and the maximum and minimumraw signal levels of the modulation scheme. The intermediate raw signalamplitude level can be calculated trigonometrically from the exhibitedminimum and maximum levels, as mentioned. If the modulation order ishigher than 16QAM, the intermediate levels can be calculated as well,assuming the branch amplitudes are equally spaced apart, as isconventional. The set of raw signal amplitude and phase levels derivedfrom the demodulation reference constitutes the calibration set, and themessage elements can be demodulated by comparison with the predeterminedamplitude levels of the calibration set. Alternatively, the message maybe demodulated by comparing the message element I and Q branchamplitudes to the other calibration set, containing the branch amplitudelevels. The two approaches should indicate the same state of themodulation scheme, and any inconsistency may indicate some kind ofpathological interference or a reception error or other mishap, and inany case the inconsistent message elements are probably faulted or atleast “suspicious”. Since the demodulation reference includes theeffects of noise and interference, the message elements may bedemodulated with the noise and interference largely mitigated, usingeither the raw-signal amplitude-phase calibration set, or the secondcalibration set based on the I and Q branch amplitudes. Therefore, ashort demodulation reference occupying just two resource elements issufficient for demodulating a message with noise and interferencecancellation.

FIG. 4B is a constellation table showing an exemplary embodiment of ashort low-complexity demodulation reference such as a 2-point short-formpulse-amplitude demodulation reference, according to some embodiments.As depicted in this non-limiting example, the table shows validmodulation states 410 of, in this case, 16QAM, with the I-branchamplitude horizontally and the Q-branch amplitude vertically. Two states412 and 413 are stippled, corresponding to the states 402, 403 of FIG.4A. The state 412 represents the first reference element of thetwo-point short-form demodulation reference, which has the maximumnegative real amplitude and the maximum positive imaginary amplitude,while the second stippled point 413 has the minimum positive realamplitude and the minimum negative imaginary amplitude. Thus thedemodulation reference exhibits the I and Q maximum and minimumamplitude levels, from which the calibration set can be found by varyingthe sign and I-Q position. The message elements may then be demodulatedby comparing each I and Q branch amplitude of each message element tothe calibration set. If the reference elements include the maximum andminimum branch amplitude levels, the two-point short-form demodulationreference provides sufficient information to generate the completecalibration set, from which the remaining amplitude and phase levels canbe calculated by interpolation, as described above. The receiver canthen fill in the amplitude levels of a calibration set and demodulate asubsequent message by comparing each message element I and Q branchamplitude to the calibration set amplitude levels, selecting the closestmatch, and thereby demodulate the message while largely canceling noiseand interference.

FIG. 4C is a phase chart showing another exemplary embodiment of a shortlow-complexity demodulation reference such as a two-point short-formpulse-amplitude demodulation reference, according to some embodiments.As depicted in this non-limiting example, the three raw signalamplitudes of 16QAM, transmitted with PAM, are shown as circles 420, andtwo particular states are shown as points 422 and 423. The first point422 exhibits the maximum positive I and Q branch amplitude levels,resulting in the largest raw signal amplitude. The second point 423 hasthe minimum positive I-branch and Q-branch amplitude levels, resultingin the smallest raw signal amplitude, also a 45-degree phase. Thereceiver can readily calculate the intermediate raw signal amplitude bytrigonometrically summing the exhibited maximum and minimum amplitudes,specifically 0.746 times the largest raw signal amplitude for 16QAM.

FIG. 4D is a constellation table showing an exemplary embodiment of ashort low-complexity demodulation reference such as a 2-point short-formpulse-amplitude demodulation reference, according to some embodiments.As depicted in this non-limiting example, the modulation states of 16QAMare shown as squares 430, and two of the modulation states are shownstippled as 432 and 433. The first state 432 exhibits the maximumpositive I and Q amplitude levels, and the second state 433 exhibits theminimum positive I and Q amplitude levels. The receiver can calculatethe other modulating states, and their raw signal or branch amplitudes,from those exhibited in the two states 432-433 of the demodulationreference. The constellation table shows the same set of states as thephase chart of FIG. 4C.

FIG. 4E is a phase chart showing an exemplary embodiment of a shortlow-complexity demodulation reference such as a two-point short-formpulse-amplitude demodulation reference for 16QAM, according to someembodiments. As depicted in this non-limiting example, the two indicatedstates 442, 443 are modulation states with the maximum raw signalamplitude, and raw signal phase of 45 degrees and 225 degrees,respectively. The receiver can calculate the minimum raw signalamplitude according to a predetermined amplitude ratio, such as 3 for16QAM, and then can calculate the intermediate raw signal amplitudetrigonometrically, as mentioned above. An advantage of the demodulationreference providing two opposite-phased maximum-amplitude referenceelements may be that the other levels and their phases can be calculatedby interpolation without the need for extrapolation, thereby minimizingcalculation errors in most cases. In addition, the I and Q branchamplitudes can be calculated from each of the two exhibited points. Afurther advantage may be that those redundant derivations can beaveraged to reduce the measurement errors. A message can then bedemodulated while largely cancelling effects of noise and interferenceaccording to the amplitude values thus obtained, according to someembodiments.

FIG. 4F is a constellation table showing an exemplary embodiment of ashort low-complexity demodulation reference such as a two-pointshort-form pulse-amplitude demodulation reference for 16QAM, accordingto some embodiments. As depicted in this non-limiting example, theconstellation table shows the 16 states 450 of 16QAM, with two of thestates 452 and 453 stippled, corresponding to the maximum positive I andQ branch amplitudes for 452, and the maximum negative I and Q branchamplitudes for 453. Thus the states 452, 453 correspond to the points442, 443 of the previous figure. The other 14 states of 16QAM can thenbe calculated deterministically from the values exhibited in the tworesource elements of the demodulation reference.

FIG. 4G is a phase chart showing an exemplary embodiment of a shortlow-complexity demodulation reference such as a two-point short-formpulse-amplitude demodulation reference for a QPSK modulation, accordingto some embodiments. As depicted in this non-limiting example, thecircle 460 represents a particular amplitude, and the two indicatedstates 462, 463 are raw signal modulation states with phase andamplitude as shown. For QPSK, the phase is varied between four valuesspaced apart by 90 degrees, and the amplitude is held constant. Thus thetwo points 462 and 463 are at the same radius 460, thereby indicatingthe same raw signal amplitude, as required for QPSK. The other twostates of QPSK can then be derived by adding 90 degrees in raw signalphase to each of the exhibited states.

FIG. 4H is a constellation table showing an exemplary embodiment of ashort low-complexity demodulation reference such as a two-pointshort-form pulse-amplitude demodulation reference for QPSK, according tosome embodiments. As depicted in this non-limiting example, themodulation table shows the four states of QPSK, with two of the states472 and 473 indicated, all at the same branch amplitude. State 472 maybe generated from the negative I-branch signal multiplexed with thepositive Q-branch signal, while the state 473 may be generated from thepositive I-branch and negative Q-branch signals. Messages modulated inQPSK can be demodulated using the two-point short-form demodulationreference by calculating the two non-exhibited states (by reversing thesigns on the various branch amplitude values), thereby determining thecomplete calibration set including the four QPSK states.

An advantage of the two-point short-form demodulation reference in PAMmay be that it is short, only two reference elements. Another advantagemay be that the two-point short-form demodulation reference may be addedto another message, even a short message, without undue consumption ofresources. Another advantage may be that the two-point short-formpulse-amplitude demodulation reference may serve as a modulationcalibration for various orders of quadrature amplitude modulation orphase-shift keying, since the receiver can readily calculate thenon-exhibited branch levels based on the branch amplitude values (or theraw signal amplitude and phase values) provided in the referenceelements of the demodulation reference. Another advantage may be thatdistortions, in amplitude or phase or both, due to noise orinterference, may be included in the amplitude and phase values of thedemodulation reference elements, and therefore those distortions may becanceled when used to demodulate a subsequent message.

FIG. 5A is a sequence chart showing an exemplary embodiment of alow-complexity procedure for providing a two-point short-formdemodulation reference, according to some embodiments. The receivedsignal is shown on the first line, a processor on the second line, andresults are shown on the third line. As depicted in this non-limitingexample, the demodulation reference is a two-point short-formpulse-amplitude demodulation reference 501, followed by a message 502which is to be demodulated. In this case, the message 502 isconcatenated directly to the demodulation reference 501, with no gap.The receiver first analyzes the demodulation reference elements andthereby determines I and Q branch amplitudes, and optionally also theraw signal amplitude and phase levels. The receiver then performs anyadditional calculations (such as interpolation or sign changes) to fillin intermediate modulation levels (if any), and accumulates thosemodulation levels in a calibration set 503. In this case, the 2-pointshort-form demodulation reference exhibits the maximum and minimum I andQ branch amplitude modulation levels. Thus the processor can determinethe in-phase and quad-phase (I&Q) branch amplitude levels of themodulation scheme.

Then, the processor analyzes each element of the message 502, byseparating the I and Q branches for each message element, comparing thebranch amplitudes to the calibration set 503, and thereby assigning areal and imaginary amplitude modulation level 504 to each of the messageelements. In addition, each amplitude level in the calibration set maybe assigned a binary code or other numerical representation, and themessage 502 may thereby be rendered as an output binary string 505. Inthis case, the message 502 is represented by a series of binary bits505, by concatenating the I and Q branch amplitude codes for eachmessage element.

FIG. 5B is a flowchart showing an exemplary embodiment of alow-complexity procedure for using a demodulation reference, accordingto some embodiments. As depicted in this non-limiting example, at 550the receiver receives a 2-point short-form PAM demodulation reference.At 551, the receiver measures the maximum and minimum branch amplitudevalues as provided in the two demodulation reference elements. At 552, aprocessor calculates any remaining amplitude levels according to thebranch amplitude levels provided explicitly in the demodulationreference. At 553, the processor fills in the branch amplitude levels ofthe modulation scheme. At 554, (if not sooner), the message is received.At 555, each message element is compared to the branch amplitudecalibration levels, thereby determining the I and Q amplitudes by whicheach message element was initially modulated. At 556, a binaryrepresentation of the message is prepared by concatenating the amplitudeand phase codes of the various message elements, and the procedure isdone at 557.

An advantage of providing a two-point short-form demodulation referencemay be that it is short, just two reference elements. Another advantagemay be that the maximum and minimum branch amplitude modulation statescan be explicitly provided and the receiver can then determine all theamplitude modulation states of the modulation scheme using theprinciples and methods disclosed, according to some embodiments. Anotheradvantage may be that distortions, in amplitude or phase or both, due tonoise or interference, may be included in the branch amplitude values ofthe demodulation reference elements, and therefore those distortions maybe canceled when those levels are then used to demodulate a subsequentmessage.

The systems and methods further include a one-point short-formdemodulation reference, with a length of just one reference element, asin the following examples.

FIG. 6A is a phase chart showing an exemplary embodiment of a very shortlow-complexity demodulation reference such as a one-point short-formdemodulation reference, according to some embodiments. As depicted inthis non-limiting example, the circles 600 represent raw signalamplitude levels, and the indicated state 601 is a modulation state atthe maximum raw signal amplitude and a raw signal phase of 135 degrees,which can be generated by multiplexing the maximum negative I-branchsignal with the maximum positive Q-branch signal. Also shown is thewidth 605 of the raw signal amplitude modulation levels 600, extendingfrom the minimum amplitude to the maximum amplitude of the raw signal.For the case shown, the maximum amplitude is 3 times the minimum. Theamplitude ratio is the ratio of the maximum raw signal amplitude leveldivided by the minimum raw signal amplitude level in the currentmodulation scheme. Alternatively, and equivalently, amplitude ratioequals the maximum positive branch amplitude level divided by theminimum positive branch amplitude level. The one-point short-formdemodulation reference may be used to demodulate elements of messagesmodulated in QAM or PSK, with pulse-amplitude modulation, so long as theamplitude ratio is known to the receiver. The amplitude ratio may bedetermined via convention, system information data, an RRC message, orotherwise.

The raw signal amplitude levels can be found according to the singledemodulation reference element and the known (maximum divided byminimum) amplitude ratio. For QPSK, the amplitude ratio is 1.0, andthere is no amplitude modulation. Conventionally, if the amplitude ratiois 3, the modulation scheme is 16QAM, 7 for 64QAM, and 15 for 256QAM. Inaddition, the receiver can calculate the maximum branch amplitude equalto the raw signal amplitude times 0.707, and then can calculate theminimum branch amplitude according to the amplitude ratio, and then canderive the other branch amplitude values by interpolation. Therefore, ademodulation reference of a single modulated point is sufficient todetermine all of the I-Q branch amplitudes and the raw signal amplitudeand phase levels, and therefore all the modulation states, of amodulation scheme, including PSK and QAM type modulation schemes. Sincethe single reference element exhibits the maximum I and Q branchamplitude values, including the effects of attenuation and receiversensitivity, the calibration set may also include those factors, andtherefore enable demodulation of the subsequent message. In addition,the receiver can measure the effects of noise and interference bycomparing the I-branch amplitude to the Q-branch amplitude. For thestate 601, those two amplitudes should be equal in magnitude andopposite in sign, if there is no additive noise. The presence of noisecan be quantified by adding the two branch amplitude values and dividingby two. That noise level can then be added to each of the branchamplitude levels of the modulation scheme to mitigate additive noise inthe subsequent message.

The one-point short-form pulse-amplitude demodulation reference istherefore able to provide a complete calibration set including all ofthe states and levels of the modulation scheme, including signalattenuation, receiver sensitivity, and additive noise or interference,when analyzed as described, according to some embodiments.

FIG. 6B is a constellation table showing an exemplary embodiment of avery short low-complexity demodulation reference such as a one-pointshort-form demodulation reference, according to some embodiments. Asdepicted in this non-limiting example, the table shows the sixteenstates 610 of 16QAM with pulse-amplitude modulation. One state 611 isstippled, corresponding to the state 601 shown in the previous figure.The state 611 corresponds to the maximum negative I branch signalmultiplexed with the maximum positive Q branch signal. Thus the twocharts of FIGS. 6A and 6B show the same information but in differentforms. Messages modulated in 16QAM can be demodulated using the depictedconstellation table, as long as the amplitude ratio is known. Themagnitudes of the branch amplitudes include the effects of attenuationand receiver sensitivity, while the difference in magnitudes is ameasure of additive noise or interference, assuming the I and Q branchesare affected in the same way (that is, no pathological orphase-dependent or amplitude-dependent or multiplicative distortions).For higher orders of modulation, the intervening levels can be found byinterpolating, thereby filling in the calibration set including all thebranch amplitude levels of the modulation scheme.

FIG. 6C is a phase chart showing another exemplary embodiment of a veryshort low-complexity demodulation reference such as a one-pointshort-form PAM demodulation reference, according to some embodiments.The one-point demodulation reference may be used to calibrate the I andQ branch amplitude levels, and/or the raw signal amplitude and phaselevels, by which the message elements of messages are modulated. Asdepicted in this non-limiting example, the circles 620 represent the rawsignal amplitude levels. Unlike the previous example, the indicatedstate 621 is modulated at the minimum raw signal amplitude and a rawsignal phase of 45 degrees. Also shown is the width of the amplitudelevels as 625, extending from the minimum raw signal amplitude to themaximum raw signal amplitude. For the case shown, the amplitude ratio(maximum/minimum) is 3; hence the maximum raw signal amplitude levelequals the exhibited minimum amplitude level times the amplitude ratio.The remaining amplitude levels may be calculated by interpolationbetween the minimum and maximum raw signal values. Alternatively, or inaddition, the I and Q branch amplitudes can be found by dividing themaximum and minimum raw signal amplitudes by 1.414 as described above.

FIG. 6D is a constellation table showing an exemplary embodiment of avery short low-complexity demodulation reference such as a one-pointshort-form demodulation reference in PAM, according to some embodiments.As depicted in this non-limiting example, the table shows the sixteenstates 630 of 16QAM, with one state 631 stippled, corresponding to thestate 621 shown in the previous figure. The state 631 corresponds to theminimum positive I-branch amplitude multiplexed with the minimumpositive Q-branch amplitude. Thus the two charts of FIGS. 6C and 6D showthe same information but in different forms. From the provided amplituderatio and the known modulation scheme, the receiver can fill in all ofthe modulation states 630 according to the exhibited minimum branchamplitudes. Messages modulated in 16QAM, or other order of quadratureamplitude modulation, as well as BPSK and QPSK, can then be demodulated.

FIG. 6E is a phase chart showing another exemplary embodiment of a1-point short-form pulse-amplitude demodulation reference, according tosome embodiments. As depicted in this non-limiting example, thedemodulation reference includes a single reference element 641positioned at a raw-signal phase of 18.4 degrees. For 16QAM, thereceiver can calculate the maximum raw-signal amplitude as 1.340 timesthe observed amplitude of the raw signal of the reference element 641,and also the minimum raw-signal amplitude as 0.447 times the observedamplitude. Likewise, the receiver can calculate that the maximum branchamplitude is 0.948 times the observed amplitude, and the minimum branchamplitude is 0.316 times that amplitude, assuming the amplitude ratio(max/min) is 3.0, as is standard for 16QAM. As mentioned, the additivenoise can be quantified by comparing the magnitude of the I-branchamplitude with three times the magnitude of the Q-branch amplitude. Forhigher orders, other ratios apply. Thus the intermediate raw amplitudelevel is the trigonometric sum of the minimum and maximum raw amplitudesin each case. From the single resource element of the 1-pointdemodulation reference, the receiver can calculate the maximum andminimum raw or branch amplitudes, and can fill in all of the modulationlevels in a calibration set assuming either PAM or raw-signalamplitude-phase analysis, and can then demodulate the message withattenuation and receiver sensitivity effectively compensated, and withadditive noise largely compensated.

FIG. 6F is a constellation table showing another exemplary embodiment ofa 1-point short-form pulse-amplitude demodulation reference, accordingto some embodiments. As depicted in this non-limiting example, a singlereference element 651 includes the maximum positive I-branch signal andthe minimum positive Q-branch signal. The receiver can separate theI-branch and Q-branch signals, measure their branch amplitudes, andthereby determine the maximum and minimum branch amplitudes of themodulation scheme, which is 16QAM. The receiver can then fill in all ofthe predetermined branch amplitude levels of the modulation scheme bymultiplying those values by plus or minus one. In addition, the receivercan calculate the raw-signal maximum, intermediate, and minimumamplitudes, and their phases, according to the trigonometric ratios of16QAM in this case, or the appropriate ratios for higher ordermodulation schemes. The receiver can then fill in all of the raw-signalamplitude and phase levels in a second calibration set. The receiver canthen demodulate a subsequent message, fully compensating for attenuationand receiver sensitivity and additive noise, by comparing each messageelement to the predetermined modulation levels in either the first orsecond calibration set, and thereby determine the message content, basedon a demodulation reference occupying just a single resource element.

FIG. 6G is a phase chart showing an exemplary embodiment of a very shortlow-complexity demodulation reference such as a one-point short-formpulse-amplitude demodulation reference for QPSK, according to someembodiments. As depicted in this non-limiting example, the circle 660represents the constant amplitude of the raw signal in this modulationscheme. The indicated state 661 is modulated at the single raw signalamplitude and at a phase of 45 degrees. The width of the amplitudelevels is zero in this case, which informs the receiver that themodulation scheme is PSK and not QAM, and therefore all of the messageelements should have the same raw signal amplitude. The receiver canfill in the calibration set by advancing the observed reference element661 by steps of 90 degrees.

FIG. 6H is a constellation table showing an exemplary embodiment of alow-complexity demodulation reference such as a one-point short-formdemodulation reference, according to some embodiments. As depicted inthis non-limiting example, the table shows the four states 670 of QPSKas I-branch amplitude versus Q-branch amplitude, with one state 671stippled, corresponding to the state 661 shown in the previous figure.The state 671 corresponds to the single positive I-branch amplitudelevel, multiplexed with the single positive Q-branch amplitude level.Thus the two charts of FIGS. 6E and 6F show the same information but indifferent forms. The receiver can fill in the predetermined branchamplitude levels (I and Q, positive and negative) based on the observedbranch amplitudes in the single reference element 671. For improvedprecision, the receiver can average the I and Q branch amplitudesmeasured from the single reference element.

An advantage of the one-point short-form demodulation reference may bethat it is very small, just one reference element, and thus can be addedto messages with only a very slight increase in resource usage. Anotheradvantage may be that it may be easy for receiver processors to use theshort-form demodulation reference to demodulate messages, using thepredetermined amplitude levels in the calibration set. Another advantagemay be that distortions, in amplitude or phase or both, due toattenuation or receiver sensitivity, may be included in the I and Qbranch amplitude values (or the raw signal amplitude and phase)exhibited in the single reference element, and therefore thosedistortions may be substantially canceled when the demodulationreference is used to demodulate a subsequent message. In addition, forcertain versions of the one-point demodulation reference, the additivenoise may be quantified and mitigated in the message demodulation.

FIG. 7A is a sequence chart showing an exemplary embodiment of alow-complexity procedure for providing and using a one-point short-formdemodulation reference, according to some embodiments. A received signalis shown on the first line, a processor on the second line, and a resultis shown on the third line. As depicted in this non-limiting example, anamplitude ratio 700, equal to the maximum branch amplitude level in themodulation scheme divided by the minimum, is initially provided (forexample, by convention, or in system information files, or as an RRCmessage). A demodulation reference 701 is later received, in this case aone-point short-form demodulation reference 701, followed later by amessage 702 which is to be demodulated. The short-form demodulationreference 701 is not time-synchronized with the message 702 in thiscase, other than to precede the message 702. In some embodiments, theamplitude-ratio message 700 may also indicate whether the short-formdemodulation reference 701 exhibits the minimum or maximum amplitudelevel of the modulation scheme. In other embodiments, that amplitudeinformation may be established by a system information message, or byconvention, or otherwise. In each case, the processor can determine howto use the amplitude ratio 700 to calculate the other, non-exhibited,amplitude levels.

The processor then analyzes the sole reference element of the one-pointshort-form demodulation reference 701 using the provided amplitude ratio700, and thereby determines the minimum branch amplitude level (if themaximum is exhibited in the demodulation reference), and completes thecalibration set 703 with all the states of the modulation scheme and thesingle branch amplitude. In this example, the 1-point short-formdemodulation reference includes the maximum positive I and maximumnegative Q branch amplitude levels. Therefore the levels of thecalibration set can compensate for additive noise in the messageelements.

Then, the processor analyzes each resource element of the message 702,comparing each I and Q branch amplitude of each message element to thecalibration set 703, and thereby assigns a modulation state 704 to eachof the message elements 702. Then each amplitude and phase modulationlevel may be assigned a binary code, or other numerical code, and theentire message 702 can then be represented by a series of binary bits705 by concatenating, or otherwise combining, the codes for each messageelement.

FIG. 7B is a flowchart showing an exemplary embodiment of alow-complexity procedure for using a demodulation reference, accordingto some embodiments. As depicted in this non-limiting example, areceiver compares elements of a message to calibrations based on aone-point short-form PAM demodulation reference, and thereby determinesthe modulation levels, in amplitude and phase, for each of the messageelements.

At 750, the receiving entity either obtains or already knows theamplitude ratio, which is the ratio of the minimum to maximum branchamplitude levels of the modulation scheme that the message is modulatedin. The amplitude ratio may be a standard convention and built-in forexample, or it may be provided from an information source such as anetwork database, or provided as part of a system information message ora RRC message, or otherwise available to the receiving entity. If themodulation scheme is QPSK, the amplitude ratio is 1.0, and there is noamplitude modulation. At 751, the receiving entity receives a one-pointshort-form demodulation reference (such as that of FIG. 6A) and, at 752,measures the maximum positive I and Q branch amplitude values asexhibited in the short-form demodulation reference. At 753, thereceiving entity calculates a minimum branch amplitude levels bydividing the maximum branch amplitudes by the amplitude ratio. At 754,the entity calculates any intermediate branch amplitude levels, if any,by interpolation. The receiver may also determine a raw signal amplitudeand phase from the received demodulation reference signal, and maycompare that determination to the branch amplitudes for consistency. Thereceiver may also compare the I and Q branch amplitudes to reveal otherinconsistencies. The receiver may average the I and Q branch amplitudesfor improved accuracy, according to some embodiments. For example, thereceiver may separate the I and Q branches of the single demodulationreference element, and measure the I branch amplitude and Q branchamplitude. Then, the receiver may demodulate the message using thosebranch amplitude values, or the receiver can average the two branchamplitude values and use that average for both the I and Q branchdemodulation of each message element. An advantage of using differentbranch amplitudes for the message I and Q demodulation may be tocompensate for phase-dependent interference, which can affect the twobranch amplitudes differently. An advantage of averaging the two branchamplitude values may be to obtain a more accurate value.

At 755 the receiver receives the message to be demodulated. At 756, thereceiver separates the I and Q branches for each message element andmeasures their branch amplitudes. At 757, the receiver compares eachbranch amplitude value to the amplitude levels in the calibration setand determines the closest modulation state. At 758, the receiverassigns a binary representation to each message element based on itsbest-match modulation state, and provides the result to an interpreterprocessor, and is done at 759.

An advantage of providing a one-point short-form demodulation referencemay be that it is very short, just one reference element. Anotheradvantage may be that the maximum or minimum positive or negative branchamplitude levels can be explicitly provided in the short-formpulse-amplitude demodulation reference, from which the other levels canbe calculated according to the known amplitude ratio. Another advantagemay be that attenuation and receiver sensitivity may be compensated whenthe received reference values are used to demodulate a subsequentmessage. Another advantage may be that the receiver can measure theamplitude and phase of the raw signal and compare those values to thebranch amplitudes to reveal complex interference or inconsistencies,according to some embodiments. Another advantage may be that, if thedemodulation reference includes a maximum branch amplitude in one of thebranches and a minimum branch amplitude in the other branch, thereceiver can determine the maximum and minimum branch amplitude levelsfrom those measurements, without the need for an amplitude ratio orother convention, according to some embodiments. Another advantage maybe that the magnitudes of the branch amplitudes may indicate the netattenuation and receiver sensitivity of the demodulation reference,enabling demodulation of the subsequent message. Another advantage maybe that, if both positive and negative branch amplitudes are exhibitedin the demodulation reference, the additive noise or interference can bequantified by the difference, and thereby mitigated in the subsequentmessage elements, according so some embodiments.

FIG. 8A is a modulation table showing an exemplary embodiment of apulse-amplitude modulation scheme, plotted according to the phase andamplitude of the raw signal, according to some embodiments. As depictedin this non-limiting example, a modulation table 800 is an array ofmodulation states of a modulation scheme, arranged according to thephase and amplitude of the as-received raw signal. The amplitude andphase of the raw signal may provide information about noise andinterference more readily and/or more precisely than amplitude analysisof the I and Q branches of PAM, and comparison of the two demodulationprocedures may reveal faulted message elements, in some embodiments.

The depicted modulation scheme in this case is 16QAM, transmittedaccording to pulse-amplitude modulation, and the raw signal is thenanalyzed by the receiver according to classical amplitude and phaseanalysis of the raw signal. Each modulation state is depicted as a dot801. (The peculiar and non-uniform distribution of states 801 in thischart is due to the effects of trigonometrically adding two sinusoidalwaves at different phases and amplitudes.) Although each raw signalmodulation state 801 is deterministically determined by the I and Qbranch amplitudes, and vice-versa, the two demodulation schemes may havedifferent sensitivities or measurement uncertainties for actual noiseand interference, particularly regarding phase errors which PAM does notmeasure. In addition, none of these measurements is perfect, and none ofthe theoretical conclusions is without assumptions. Therefore, the rawsignal amplitude and phase may provide distinct or at least improvedinformation about the proper demodulation value of each message element,and may reveal which message elements are faulted in case the message isdetermined to be corrupted. Accordingly, in some embodiments, thedemodulation reference and each message element may be analyzed by bothmethods, including amplitude determination of the separate I and Qbranches, and amplitude-phase analysis of the raw signal. Those resultsmay be combined by, for example, allocating a message element to a“suspicious” category if the message element has poor modulationquality, by either PAM analysis or raw signal amplitude-phasedetermination, and especially if the two procedures indicate differentmodulation states for the same message element.

The chart shows, around each state 801, a “good-modulation” zone 802 indark stipple and a larger “marginal-modulation” zone 803 in lightstipple, while the exterior space 808 is relegated to a “bad-modulation”zone. Message elements in which the raw signal amplitude and phase occurin the marginal 803 or bad modulation 808 zones may thereby reveal whichmessage elements in a corrupt reception are at fault. In someembodiments, the receiver may test each message element according to theamplitude and phase properties of the raw signal, then separate the Iand Q branches and test each of them for agreement with one of thepredetermined branch amplitude levels, and thereby flag a messageelement as suspicious if the message element appears in the bad ormarginal modulation zone according to either the raw signal analysis orthe branch analysis. In addition, the message element is likely faultedif the two demodulation techniques produce inconsistent results, inwhich PAM indicates a different modulation state than amplitude-phasedemodulation.

In addition, the receiver may apply a similar check to the elements of ademodulation reference, such as a four-point or two-point or one-pointshort-form pulse-amplitude demodulation reference. For example, thereceiver can determine whether the raw signal amplitude and phase valuesof each demodulation reference element are consistent with their I and Qbranch amplitudes. In addition, the receiver may flag as suspicious ademodulation element that exhibits a raw signal amplitude or phase thatdiffers substantially from the same parameters in a previousdemodulation reference, and may thereby detect a sudden change inbackgrounds. The receiver may reveal suspicious message elements ordemodulation reference elements that may be missed if tested using onlya single analysis type.

The chart also shows a particular state 805, with maximum raw-signalamplitude and 315-degree raw-signal phase. This state 805 corresponds tothe sum-signal wave 103 of FIG. 1A.

The chart also shows another particular state 806, with maximalraw-signal amplitude and 135-degree raw-signal phase. This state 806corresponds to the one-point demodulation reference 601 of FIG. 6A.

The chart also shows two more states, 809 and 810, corresponding to thestates 422 and 423, respectively, of FIG. 4C.

The chart also shows another state 804 with mixed amplitude and a phaseof just 18.4 degrees. This corresponds to the one-point short-formpulse-amplitude demodulation reference of FIG. 6E or 6F.

A demodulation reference with a single reference element modulated withthe maximum branch amplitude level in one branch and the minimum branchlevel in the other branch can therefore determine both levels byseparating the two branches, measure the maximum and minimum branchamplitudes therein, and then calculate all of the other PAM amplitudelevels of the modulation scheme from those values. In addition, thereceiver can also calculate the raw signal amplitude and phase levelsfrom the branch amplitudes and the raw signal phase. Specifically,referring again to state 804, the maximum raw signal amplitude level isequal to 1.414 times the I-branch amplitude, and the minimum raw signalamplitude is 1.414 times the Q-branch amplitude of that state, andsimilar ratios exist for the other mixed-amplitude states. In addition,the intermediate raw signal amplitude is already provided by theas-received demodulation reference signal, with no further analysisneeded other than measuring the received signal amplitude. In addition,the receiver can compare each message element's raw signal amplitude andphase to the amplitude and phase levels calculated from the demodulationreference such as that of FIG. 6E or 6F, and thereby determineinconsistencies between the PAM demodulation and the raw signaldemodulation, indicating some kind of phase-dependent noise or othererror. Faulted message elements, for example, may be revealed by suchinconsistencies.

FIG. 8B is a modulation table 820 showing an exemplary embodiment of afour-point demodulation reference modulated according to apulse-amplitude modulation scheme and displayed according to theraw-signal phase and amplitude, according to some embodiments. Asdepicted in this non-limiting example, the modulation states 821 areshown as dots, with the raw signal amplitude vertical and the raw signalphase horizontal. Certain states are surrounded by a good-modulationzone 822 in dark stipple. These states 824, 825, 826, 827 correspond tothe same states 224, 225, 226, 227 of FIG. 2C, or the correspondingstates 234, 235, 236, 237 of FIG. 2D. Thus the demodulation referenceelements of a four-point short-form pulse-amplitude demodulationreference can be reanalyzed according to the raw signal phase andamplitude, and displayed as shown in this figure. Each of the short-formdemodulation reference examples discussed above, as well as otherdemodulation references for other modulation schemes, may be reanalyzedaccording to the raw signal properties in a similar way, potentiallyrevealing otherwise unseen noise or interference or inconsistencies orother problems that may cause message demodulation errors, according tosome embodiments.

FIG. 9 is a flowchart showing an exemplary embodiment of a process forchecking a demodulation reference, which is configured inpulse-amplitude modulation and analyzed according to the phase andamplitude of the raw signal, according to some embodiments. As depictedin this non-limiting example, at 901 a receiver receives a demodulationreference, such as one of the short-form pulse-amplitude demodulationreferences disclosed herein, or another type. At 902, the receivermeasures the raw signal amplitude and phase for each reference elementof the demodulation reference, and at 903 calculates any furtherintervening amplitude and phase levels of the modulation scheme by, forexample, interpolation. The receiver then fills in the amplitude andphase levels of a first calibration set representing the states of themodulation scheme in amplitude and phase modulation of the raw signal.

At 904, the receiver re-analyzes the elements of the demodulationreference, this time separating the I and Q branches and measuring thebranch amplitudes. At 905, the receiver calculates any interveningbranch amplitudes and fills in the amplitude levels of a secondcalibration set including all of the branch amplitudes of the modulationscheme. At 906, the receiver checks for inconsistencies between thestate assignments of the first and second calibration sets, which mayindicate pathological interference or measurement errors or phase errorsor other problems, and if so, drops to 912 and requests aretransmission.

At 907, the receiver receives a message and, at 908, measures the rawsignal amplitude and phase of each message element. The receiverdetermines the modulation state by selecting the closest amplitude andphase levels of the first calibration set. At 909, the receiverre-analyzes the message elements by separating the I and Q branches andmeasuring each branch amplitude, and then determines the modulationstate by selecting the closest branch amplitude levels in the secondcalibration set. At 910, the receiver checks for inconsistent stateassignments by the two demodulation procedures, and if so, drops to 912to request a retransmission of the message as well as the demodulationreference. If no such errors are uncovered, then at 911 it conveys themessage data, representing the modulation states of each messageelement, to an interpretation processor and is done.

In some embodiments, the receiver may determine that one or a smallnumber of the message elements are faulted according to the consistencycheck, and instead of requesting a retransmission, may attempt torecover the message by altering the state assignments of the likelyfaulted message elements. For example, the receiver can alter theassigned states of the suspicious elements to other adjacent states(differing by one branch amplitude level, or by one raw signal amplitudelevel, or one raw signal phase level, for example), and if that is notsuccessful, to the other states of the modulation scheme, while testingeach candidate message against an error-detection code (such as a CRC orother error code) which may be embedded in the message. If the message,with such an altered state assignment, then agrees with theerror-detection code, the message has been recovered. If all of thefeasible alterations fail to agree with the error-detection code, thenthe receiver may request the retransmission.

By checking the signal properties according to two differentdemodulation schemes, the receiver may detect faults and/or identify thelikely faulted message elements, due to the different properties anddistortion sensitivities of the two demodulation schemes, according tosome embodiments.

FIG. 10A is a sketch showing an exemplary embodiment of a resource grid1000 according to some embodiments. One slot is indicated as 1001 andone resource block as 1002. Symbol times are marked as 1004 andsubcarriers as 1005. A single resource element is shown as 1007. Thefirst symbol time of each slot is outlined. As depicted in thisnon-limiting example, a message 1009, shown in stipple, isfrequency-spanning in the fifth symbol period. Demodulation references1008, shown in grid hatch, are two-point short-form pulse-amplitudedemodulation references in this case. Each demodulation reference 1008occupies just two resource elements, inserted among the messageelements. In this case, the demodulation references appear in the firsttwo subcarriers of the frequency-spanning message, in each resourceblock, throughout the message 1009. Each two-point short-formdemodulation reference 1008 includes sufficient amplitude and phaseinformation to update all of the amplitude and phase levels of thecalibration set in the presence of current interference, and therebyimproves the interference mitigation of the message 1009. Importantly,the average distance (in frequency) from each message element to theclosest demodulation reference is only 3 subcarriers, yet the additionalresource usage is less than 17%. The figure thus demonstrates thatinserting a two-point short-form demodulation reference 1008 in eachresource block of a frequency-spanning message 1009 providesrecalibrations of modulation levels close to the message elements forimproved interference mitigation, yet causes only a small increase inresource and energy usage, according to some embodiments.

FIG. 10B is a sketch showing an exemplary embodiment of a resource grid1050 according to some embodiments. As depicted in this non-limitingexample, the resource grid 1050 includes three slots and one resourceblock. Two time-spanning messages are shown in subcarriers 1 and 9. Eachmessage is interspersed with one-point short-form pulse-amplitudedemodulation references. A first message 1059 includes a one-pointdemodulation reference 1058 in the first symbol period of each slot. Theone-point demodulation references 1058 thereby provide sufficientmodulation information to refresh the calibration set on the time scaleof one slot, at a cost of only about 7% of the message resourceelements.

The figure also shows a second message 1069 in the ninth subcarrier. Thesecond message 1069 is interspersed by one-point short-formpulse-amplitude demodulation references 1068 in every seventh symboltime, thereby providing interference mitigation on a time scalecorresponding to a half-slot, for a resource usage increase of about14%. The average distance from a message element to the nearestdemodulation reference is reduced to 2 symbol periods in the depictedexample. Such close proximity between message elements and demodulationreferences thereby provides further improved interference mitigation.

The improved local demodulation information provided in the one-pointshort-form demodulation references 1008 or 1058 or 1068 may be employedin various ways. In one embodiment, the receiver may be configured todemodulate each portion of the message 1009 or 1059 or 1069 according tothe updated modulation levels provided by the immediately precedingdemodulation reference 1008 or 1058 or 1068. In that case, each portionof the message 1009 or 1059 or 1069 is demodulated according to theimmediately preceding demodulation reference 1008 or 1058 or 1068.

In a second embodiment, the receiver may be configured to demodulateeach portion of the message 1009 or 1059 or 1069 by averaging the twoshort-form demodulation references 1008 or 1058 or 1068 adjacent to thatmessage portion, that is, by averaging the corresponding modulationlevels in the demodulation references 1008 or 1058 or 1068 immediatelypreceding and immediately following each message portion 1009 or 1059 or1069. For example, the receiver may average the I or Q branch amplitudelevels in the preceding and following demodulation references 1008 or1058 or 1068, and then may demodulate the intervening message portionaccording to those average amplitude levels. By accounting forinterference at both ends of each message portion, the receiver maymitigate variable interference more accurately than using just thepreceding demodulation reference to demodulate the message portion.

In a third embodiment, the receiver may be configured to calculate aweighted average for each amplitude and phase level in the modulationscheme. The weighted average may be obtained by weighting theimmediately preceding and immediately following short-form demodulationreferences. The weighting may be according to the distance, in time orfrequency, between each message element and the two proximatedemodulation references. For example, the calibration set for eachmessage element may be calculated by interpolating between the precedingand following demodulation references. For example, the receiver maydemodulate a particular message element that is in the middle of themessage portion (and hence equidistant from the preceding and followingdemodulation references) by weighting the preceding and following valuesequally. For the first message element in the message portion, on theother hand, the preceding demodulation reference may be weighted heavily(since it is closer) and the following demodulation reference may beweighted only lightly. Likewise, for the last message element in amessage portion, the receiver may heavily weight the followingdemodulation reference and lightly weight the preceding one. In thisway, the receiver may interpolate between the preceding and followingdemodulation reference, and thereby calculate a distance-weightedcalibration set associated with each message element according to itsdistance from the preceding and following demodulation references, andthen may demodulate each element of the message using that weightedaverage. The resulting demodulation may thereby mitigate variableinterference more effectively than a non-weighted average.

In a fourth embodiment, the receiver may be configured to average aplurality of the preceding demodulation references, and optionally oneor more of the following demodulation references as well, in order toobtain a more accurate determination of the levels of the modulationscheme. Averaging multiple demodulation references may provide a moreprecise determination of the correct demodulation levels when there israndom noise in the receiver, such as electronic noise, which is thenamplified in the amplifier of the receiver. In some cases, noise may berelatively stable or slowly changing in time or frequency, in which casethe averaging of several of the short-form demodulation references mayprovide a more precise determination of the levels despite measurementerrors.

Interference, on the other hand, is generally highly structured infrequency and time because it is likely due to competing messages fromadjacent cells, or from electrical machinery or the like. Averagingmultiple short-form demodulation references may be counter-productivewhen frequency-rich interference is larger than noise, because suchinterference generally changes rapidly in time and/or in frequency,thereby likely changing shorter than the averaging time (or averagingfrequency band) of the short-form demodulation references, then thoseaveraged demodulation levels are likely to be incorrect when applied tothe subsequent message elements. Therefore, when interference is greaterthan noise, the weighted-average embodiment described above, involving aweighted average between two short-form demodulation references thatprecede and follow the message section, may provide better mitigationand fewer message faults, than averaging multiple preceding and multiplefollowing demodulation references. In contrast, when noise is greaterthan interference (and is sufficiently stable in time or frequency),then the averaging of multiple short-form demodulation references mayprovide a more accurate set of level values than a single short-formdemodulation reference.

In some embodiments, a formula may be provided to assist user devicesand base stations in deciding which type of averaging is expected toresult in fewest message faults, according to the current conditions.Conditions that may affect the choice may include factors such as thetraffic density, the prior fault rate, the average noise amplitude, themaximum range of interference fluctuations, and the like. The formulamay be based on machine learning and/or artificial intelligence. Theformula may be configured to provide, as output, the most suitable typeof averaging or interpolating of short-form demodulation referencevalues, according to the current network and background and messagingconditions. For example, if noise dominates, the formula may recommendaveraging multiple short-form demodulation references to obtain a moreaccurate value of each modulation level, whereas if interferencedominates, the formula may recommend not averaging at all, or else usingthe weighted averaging based on distance from the preceding andfollowing short-form demodulation references. In this way, the formulamay assist the receiver in mitigating both electronic noise andfluctuating interference while minimizing message faults under bothconditions.

In some embodiments, a short-form demodulation reference may indicatethe beginning and/or ending of a message. User devices often havedifficulty identifying downlink control messages due to the large numberof possible positions and sizes of the messages. User devices areexpected to test all of the possible combinations of starting locationand length of possible downlink control messages by unscrambling eachcandidate message and comparing to an included error-detection code, forexample. The short-form demodulation reference can greatly simplify thisprocess by indicating, with a characteristic pattern of referenceelements, the beginning and/or ending of a message. For example, atwo-point short-form demodulation reference having the maximum branchamplitudes in its first reference element and the minimum branchamplitudes in its second reference element, can be placed at the startof the message, to indicate where the message begins. The end of themessage may be indicated by another, optionally different, pattern ofshort-form demodulation reference, such as the minimum branch amplitudesfollowed by the maximum branch amplitudes. The receiver may beconfigured to search for the beginning and ending patterns among thereceived elements, and thereby identify messages, or at least greatlyreduce the number of candidate messages that the receiver needs to test.In addition, the two-point short-form demodulation references at thebeginning and ending of the message may assist in demodulating themessage.

An advantage of providing multiple short-form pulse-amplitudedemodulation references, such as one-point or two-point short-formdemodulation references, interspersed among portions of a message, maybe that the modulation levels of the message elements may berecalibrated frequently thereby, resulting in interference mitigation onshort time and frequency scales. In a dense radio environment, withlarge numbers of devices transmitting on various frequencies at varioustimes, message faults may be reduced by providing demodulationrecalibrations in close proximity to the message elements they areintended to demodulate. Use of a short demodulation format, such as ashort-form demodulation reference occupying just one or two resourceelements, may minimize the additional energy consumed andelectromagnetic background generated. Another advantage may be thatdistortions, in amplitude or phase or both, due to noise orinterference, may be included in the amplitude and phase values of thereference elements, and therefore those distortions may be canceled in asubsequent message demodulated using those reference values.

Numerous versions of short-form demodulation references are disclosedherein, each with different properties, and many others are possibleusing the mathematical relationships discussed, or other equivalentmathematical relationships. Selecting which one to use in any messagingsituation is a complex problem. An algorithm may be developed to selectan appropriate or optimal type of short-form demodulation referencedepending on wireless conditions, the message, capabilities of thetransmitter and receiver, current traffic conditions, QoS requested, andmany other considerations. A 4-point short-form demodulation referenceprovides more information and redundancy than the 2-point version, whilethe 1-point version is very short but requires that the amplitude ratiobe predetermined. Other-point versions (3, 6, etc. points) are alsopossible. In some applications, keeping the message short may beparamount, whereas in other applications the additional redundancy andreliability of the 4-point version may be preferred. Some applicationsmay prioritize low latency, while others may require high reliability,and still others may need reduced complexity. Different versions may beoptimal for different modulation schemes, such as those with and withoutamplitude modulation. The transmitting processor may select the size andformat according to each message situation. Alternatively, a conventionmay be established favoring one of the short-form demodulation versionsas a default for all situations. As a further option, various versionsmay be recommended according to current parameters such as the energydensity and time-frequency properties of current interference.

As a further option, artificial intelligence (AI) or machine learningmay be used to prepare an algorithm, which is configured to select aparticular demodulation reference version according to the messagingsituation. To prepare such an algorithm, a large number of messagingevents may be tracked (or recorded or analyzed) by one or more basestations (or core networks or other networking entities). The data maybe analyzed by an AI structure such as a neural net, which takes ininput parameters and calculates output values according to a number ofinternal variables which are adjustable. For example, the inputparameters may include the current traffic density, number of activelycommunicating user devices, average size of messages, amount and type ofexternal interference, the size and type of short-form demodulationreference employed in various messaging situations, and the QoSrequirements related to each message, as well as a measure of theresulting network performance. The AI structure may also take as inputthe expected costs, such as resource element usage, delays, subsequentmessage failures, and the like. The AI structure may be configured togenerate outputs such as a prediction of the subsequent networkperformance, which may then be compared to the measured networkperformance, to judge how accurate the predictions are. Alternatively,the outputs may include a suggested format of a short-form demodulationreference according to current conditions, which users and base stationsmay then employ. The AI structure may also compare the costs andadvantages of the standard 5G/6G DMRS reference to the various formatsof short-form demodulation references, and may thereby address a greaterrange of use cases. The variables may then be varied to optimize, or atleast improve, the accuracy of the outputs or predictions.

An algorithm may be derived from the AI structure when the outputs haveachieved a sufficient accuracy. The algorithm may be the AI structureitself, or the AI structure condensed by freezing the variables andexcising any inputs and internal functions that have demonstrated littleeffect on the outputs, for example. Alternatively, an algorithm may beprepared to mimic the AI outputs according to the input values, butusing a different and preferably simpler calculation technique, such asan analytic function or a computer program or an interpolation table,among many other envisioned calculation options. The algorithm may thenbe provided to base stations and user devices so that they may makeoptimal, or at least improved, decisions regarding demodulationreferences according to the situation.

The algorithm may also provide assistance to the transmitter, indeciding which type of short-form demodulation reference to use, and howoften to include them in the message. For example, the algorithm maytake as input a measure of the interference levels observed at thetransmitter, other measures of interference measured by the receivingentity and communicated to the transmitter, a previously-determinedlevel of noise in the transmission process, a previously-determinedlevel of noise in the receiver and communicated to the transmitter, thespectrum of variations in noise or interference versus time or frequencyor both, among other possible considerations. The algorithm may furtherinclude receiver preferences, such as requiring high reliability ratherthan low latency, or vice versa. The length of the message, the numberof competing users, the expected traffic density and other networkparameters may also contribute to the algorithm's determination.

Due to the potentially large number of inputs and adjustable variablesin the model, and the very large amount of training data likely neededfor convergence of the model, the AI structure is preferably prepared ina supercomputer. The supercomputer may be a classicalsemiconductor-based computer, with sufficient speed and thread count andprocessor count to perform the model training in a feasible amount oftime. Alternatively, the supercomputer may be a quantum computer having“qbits” or quantum bits as its working elements. Quantum computers mayprovide special advantages to solving AI models because they can veryrapidly explore a complex terrain of values, such as the highlyinterrelated effects of the various inputs on the output results.Therefore, the systems and methods include a quantum computer programmedto include an AI structure and trained on network performance data andon input parameters including interference and noise parameters, messageparameters, and the like as discussed above.

As a further option, a wireless standards committee may select one ofthe short-form demodulation reference versions as a default standard.The selection may be based, at least in part, on the artificialintelligence or machine learning structure results or the algorithmderived from it.

For a handy universal default, the embodiment of FIG. 4A or 4B, atwo-point short-form pulse-amplitude demodulation reference showing themaximum positive and minimum negative branch amplitude values in theI-branch and Q-branch amplitudes, is offered as an advantageouscandidate for such standardization, because the receiver can calculatethe remaining branch amplitude levels of the modulation scheme accordingto the exhibited branch amplitudes, according to some embodiments. The2-point demodulation reference can mitigate additive noise andinterference according to the exhibited amplitudes. All of the branchamplitude levels of the modulation scheme can be determined from the2-point short-form pulse-amplitude demodulation reference usinglow-complexity logic and arithmetic, as described. The defaultshort-form demodulation reference can then be transmitted periodically,or prepended to messages, or prepended and appended to messages, orinterspersed multiply within longer messages.

As another possible advantage, the 2-point short-form demodulationreference, or other default, when prepended to a message, may therebyindicate exactly where the message begins, thereby greatly simplifyingdetection of incoming messages. For example, the receiver can scan theactive bandwidth for the characteristic code of the short-formdemodulation reference, such as (0100) representing the maximum andminimum positive branch amplitudes. For specificity, the samedemodulation reference may be repeated, such as (0100 0100). The end ofthe message may be indicated by an ending configurations such as (0001),indicating the minimal positive I-branch and maximal positive Q-branchamplitudes. By finding those characteristic patterns, the receiver maydetermine the starting and ending points of the message. In 5G and 6G,it is generally difficult for user devices to determine the startingpoint of a control message, absent such a characteristic initial code.In addition, for the two-point or four-point versions, the orientationof the reference elements, as time-spanning or frequency-spanning,thereby indicates whether the subsequent message is time-spanning orfrequency-spanning. For example, a sidelink message may be time-spanningor frequency-spanning according to the transmitting entity's preference.In addition, the short-form demodulation reference may be advantageouslyemployed on low-complexity or legacy channels as well ashigh-performance managed channels of 5G/6G, thereby providing compactand easy-to-use modulation calibration for each message. Moreover, thesmall size of the default short-form demodulation reference may be anenabling factor for agile interference mitigation in noisy environments,because the short short-form demodulation references may be placedliberally within messages at low cost, especially in regions withinterference problems.

The wireless embodiments of this disclosure may be aptly suited forcloud backup protection, according to some embodiments. Furthermore, thecloud backup can be provided cyber-security, such as blockchain, to lockor protect data, thereby preventing malevolent actors from makingchanges. The cyber-security may thereby avoid changes that, in someapplications, could result in hazards including lethal hazards, such asin applications related to traffic safety, electric grid management, lawenforcement, or national security.

In some embodiments, non-transitory computer-readable media may includeinstructions that, when executed by a computing environment, cause amethod to be performed, the method according to the principles disclosedherein. In some embodiments, the instructions (such as software orfirmware) may be upgradable or updatable, to provide additionalcapabilities and/or to fix errors and/or to remove securityvulnerabilities, among many other reasons for updating software. In someembodiments, the updates may be provided monthly, quarterly, annually,every 2 or 3 or 4 years, or upon other interval, or at the convenienceof the owner, for example. In some embodiments, the updates (especiallyupdates providing added capabilities) may be provided on a fee basis.The intent of the updates may be to cause the updated software toperform better than previously, and to thereby provide additional usersatisfaction.

The systems and methods may be fully implemented in any number ofcomputing devices. Typically, instructions are laid out on computerreadable media, generally non-transitory, and these instructions aresufficient to allow a processor in the computing device to implement themethod of the invention. The computer readable medium may be a harddrive or solid state storage having instructions that, when run, orsooner, are loaded into random access memory. Inputs to the application,e.g., from the plurality of users or from any one user, may be by anynumber of appropriate computer input devices. For example, users mayemploy vehicular controls, as well as a keyboard, mouse, touchscreen,joystick, trackpad, other pointing device, or any other such computerinput device to input data relevant to the calculations. Data may alsobe input by way of one or more sensors on the robot, an inserted memorychip, hard drive, flash drives, flash memory, optical media, magneticmedia, or any other type of file—storing medium. The outputs may bedelivered to a user by way of signals transmitted to robot steering andthrottle controls, a video graphics card or integrated graphics chipsetcoupled to a display that maybe seen by a user. Given this teaching, anynumber of other tangible outputs will also be understood to becontemplated by the invention. For example, outputs may be stored on amemory chip, hard drive, flash drives, flash memory, optical media,magnetic media, or any other type of output. It should also be notedthat the invention may be implemented on any number of different typesof computing devices, e.g., embedded systems and processors, personalcomputers, laptop computers, notebook computers, net book computers,handheld computers, personal digital assistants, mobile phones, smartphones, tablet computers, and also on devices specifically designed forthese purpose. In one implementation, a user of a smart phone orWi-Fi-connected device downloads a copy of the application to theirdevice from a server using a wireless Internet connection. Anappropriate authentication procedure and secure transaction process mayprovide for payment to be made to the seller. The application maydownload over the mobile connection, or over the Wi-Fi or other wirelessnetwork connection. The application may then be run by the user. Such anetworked system may provide a suitable computing environment for animplementation in which a plurality of users provide separate inputs tothe system and method.

It is to be understood that the foregoing description is not adefinition of the invention but is a description of one or morepreferred exemplary embodiments of the invention. The invention is notlimited to the particular embodiments(s) disclosed herein, but rather isdefined solely by the claims below. Furthermore, the statementscontained in the foregoing description relate to particular embodimentsand are not to be construed as limitations on the scope of the inventionor on the definition of terms used in the claims, except where a term orphrase is expressly defined above. Various other embodiments and variouschanges and modifications to the disclosed embodiment(s) will becomeapparent to those skilled in the art. For example, the specificcombination and order of steps is just one possibility, as the presentmethod may include a combination of steps that has fewer, greater, ordifferent steps than that shown here. All such other embodiments,changes, and modifications are intended to come within the scope of theappended claims.

As used in this specification and claims, the terms “for example”,“e.g.”, “for instance”, “such as”, and “like” and the terms“comprising”, “having”, “including”, and their other verb forms, whenused in conjunction with a listing of one or more components or otheritems, are each to be construed as open-ended, meaning that the listingis not to be considered as excluding other additional components oritems. Other terms are to be construed using their broadest reasonablemeaning unless they are used in a context that requires a differentinterpretation.

1. A method for demodulating a wireless message, the message comprisingmessage elements, each message element modulated according to amodulation scheme, the modulation scheme comprising integer Nlevelpredetermined amplitude levels, Nlevel greater than or equal to two, themethod comprising: receiving a demodulation reference comprising integerNref reference elements, Nref less than or equal to four; extracting,from each reference element, an I-branch signal having an I-branchamplitude, and a Q-branch signal having a Q-branch amplitude, theI-branch signal phase-shifted relative to the Q-branch signal;determining, based at least in part on the Nref I-branch amplitudes andthe Nref Q-branch amplitudes, the Nlevel predetermined amplitude levelsof the modulation scheme; and demodulating each message elementaccording to the predetermined amplitude levels.
 2. The method of claim1, wherein the demodulation reference and the wireless message aretransmitted according to 5G or 6G technology.
 3. The method of claim 1,further comprising: calculating one or more intermediate amplitudelevels, each intermediate amplitude value comprising one of thepredetermined amplitude levels, wherein each intermediate amplitudevalue is distinct from all of the I-branch amplitudes and all of theQ-branch amplitudes.
 4. The method of claim 1, further comprising:extracting, from each message element, a first branch signal and asecond branch signal, the second branch signal phase-shifted relative tothe first branch signal; measuring, according to the first branchsignal, a first amplitude value, and determining which of thepredetermined amplitude levels most closely matches the first branchamplitude value; and measuring, according to the second branch signal, asecond amplitude value, and determining which of the predeterminedamplitude levels most closely matches the second branch amplitude value.5. The method of claim 4, further comprising: associating, with eachpredetermined amplitude level, a distinct code or number; selecting afirst code or number associated with the predetermined amplitude levelmost closely matching the first amplitude value; selecting a second codeor number associated with the predetermined amplitude level most closelymatching the second amplitude value; and concatenating the first code ornumber with the second code or number.
 6. The method of claim 5, furthercomprising: for each message element, receiving a raw signal comprisingthe received signal prior to extraction of the I-branch and Q-branchsignals; measuring a raw signal amplitude and a raw signal phase of theraw signal; determining, according to the raw signal amplitude andphase, a particular modulation state of the modulation scheme; andcomparing the particular modulation state with the concatenated firstand second codes or numbers.
 7. The method of claim 1, wherein: themodulation scheme includes a minimum positive predetermined amplitudelevel and a maximum positive predetermined amplitude level; thedemodulation reference comprises exactly two reference resourceelements; one of the reference resource elements comprises a firstI-branch and a first Q-branch, both the first I-branch and the firstQ-branch modulated according to the minimum positive predeterminedamplitude level; and one of the reference resource elements comprises asecond I-branch and a second Q-branch, both the second I-branch and thesecond Q-branch modulated according to the maximum positivepredetermined amplitude level.
 8. The method of claim 1, wherein: themodulation scheme includes a maximum negative predetermined amplitudelevel and a maximum positive predetermined amplitude level; thedemodulation reference comprises exactly two reference resourceelements; one of the reference resource elements comprises a firstI-branch and a first Q-branch, both the first I-branch and the firstQ-branch modulated according to the maximum negative predeterminedamplitude level; and one of the reference resource elements comprises asecond I-branch and a second Q-branch, both the second I-branch and thesecond Q-branch modulated according to the maximum positivepredetermined amplitude level.
 9. The method of claim 1, wherein: thepredetermined amplitude levels include a maximum positive amplitudelevel and a minimum positive amplitude level; an amplitude ratio equalsthe maximum positive amplitude level divided by the minimum positiveamplitude level; the demodulation reference comprises exactly onereference resource element; the one reference resource element comprisesa first branch signal and a second branch signal, the first branchsignal phase-shifted relative to the second branch signal; and themethod further comprises: if the first branch signal and the secondbranch signal are both modulated according to the maximum positiveamplitude level, determining the minimum positive amplitude level bydividing the maximum positive amplitude value by the amplitude ratio; ifthe first branch signal and the second branch signal are both modulatedaccording to the minimum positive amplitude level, determining themaximum positive amplitude level by multiplying the minimum positiveamplitude value by the amplitude ratio; and if the first branch signalis modulated according to the maximum positive amplitude level and thesecond branch signal is modulated according to the minimum positiveamplitude level, determining the maximum positive amplitude level basedon the first branch signal and determining the minimum positiveamplitude level based on the second branch signal.
 10. The method ofclaim 1, further comprising: determining that the demodulation referencecomprises exactly one reference resource element, the one referenceresource element comprising a first branch signal and a second branchsignal phase-shifted relative to the first branch signal; determining,according to an amplitude of the first branch signal, a maximumpredetermined amplitude level of the modulation scheme; and determining,according to an amplitude of the second branch signal, a minimumpredetermined amplitude level of the modulation scheme.
 11. The methodof claim 1, further comprising: receiving, for each reference resourceelement, a raw reference signal comprising a raw reference signalamplitude and a raw reference signal phase, respectively; recording, ina calibration set, the raw reference signal amplitudes and the rawreference signal phases; receiving, for each message element, a rawmessage signal comprising a raw message signal amplitude and a rawmessage signal phase, respectively; determining, for each messageelement, which raw reference signal amplitude and which raw referencesignal phase in the calibration set most closely match the raw messagesignal amplitude and the raw message signal phase.
 12. The method ofclaim 1, further comprising: receiving a first demodulation referenceand determining a first set of predetermined amplitude levels therefrom;receiving a second demodulation reference and determining a second setof predetermined amplitude levels therefrom; then calculating a thirdset of predetermined amplitude levels by averaging the first and secondsets of predetermined amplitude levels.
 13. The method of claim 12,further comprising: receiving a message element comprising a firstbranch signal multiplexed with a second branch signal, the first branchsignal having a first branch amplitude, and the second branch signalhaving a second branch amplitude; and determining which predeterminedamplitude level, of the third set of predetermined amplitude levels,most closely matches the first branch amplitude, and determining whichpredetermined amplitude level, of the third set of predeterminedamplitude levels, most closely matches the second branch amplitude. 14.Non-transitory computer-readable media in a wireless receiver, the mediacontaining instructions that when executed by a computing environmentcause a method to be performed, the method comprising: receiving ademodulation reference comprising exactly one reference elementmodulated according to a modulation scheme, the modulation schemecomprising integer Nlevel amplitude levels, the amplitude levelsincluding a minimum positive amplitude level and a maximum positiveamplitude level, wherein a predetermined amplitude ratio equals themaximum positive amplitude level divided by the minimum positiveamplitude level; extracting, from the reference element, a first branchsignal having a first branch amplitude, and a second branch signalhaving a second branch amplitude, the second branch signal phase-shiftedrelative to the first branch signal; and setting the maximum positiveamplitude level equal to the first branch amplitude and the minimumpositive amplitude level equal to the second branch amplitude.
 15. Themedia of claim 14, the method further comprising: calculating zero ormore intermediate amplitude levels by interpolating between the maximumpositive amplitude level and the minimum positive amplitude level;accumulating the maximum positive amplitude level, the minimum positiveamplitude level, the zero or more intermediate amplitude levels, and anegative of each listed amplitude level, in a calibration set; anddemodulating a wireless message according to the calibration set. 16.The media of claim 15, wherein the demodulating comprises: for eachmessage element of the wireless message, separating an I-branch signalhaving an I-branch amplitude and a Q-branch signal having a Q-branchamplitude, the I-branch signal phase-shifted relative to the Q-branchsignal; and comparing the I-branch amplitude to the amplitude levels inthe calibration set and comparing the Q-branch amplitude to theamplitude levels in the calibration set.
 17. The media of claim 16, themethod further comprising: measuring a raw reference amplitudecomprising an amplitude of the reference element and a raw referencephase comprising a phase of the reference element; calculating zero ormore additional raw reference amplitudes according to the predeterminedamplitude ratio, and calculating one or more additional raw referencephases according to a predetermined phase step; accumulating the rawreference amplitude, the additional raw reference amplitudes, the rawreference phase, and the additional raw reference phases in a secondcalibration set; for each message element, measuring a raw signalamplitude comprising an amplitude of the message element, and measuringa raw signal phase comprising a phase of the message element; and foreach message element, selecting which of the raw reference amplitudesand raw reference phases in the second calibration set most closelymatches the raw signal amplitude and the raw signal phase.
 18. The mediaof claim 17, the method further comprising: determining, according tothe comparing, a first modulation state of the modulation scheme;determining, according to the selecting, a second modulation state ofthe modulation scheme; and determining, if the first and secondmodulation states are different, that an error has occurred.
 19. Awireless communication device configured to: receive a demodulationreference modulated according to a modulation scheme, the modulationscheme comprising integer Nlevel predetermined amplitude levels, thedemodulation reference comprising exactly two reference resourceelements, each reference resource element comprising a first branchsignal and a second branch signal phase-shifted relative to the firstbranch signal; determine four reference amplitude values according tothe first and second branch signals of the two reference resourceelements, respectively; and determine the Nlevel amplitude levelsaccording to the four reference amplitude values.
 20. The wirelesscommunication device of claim 19, further configured to: receive amessage comprising message elements, each message element modulatedaccording to the modulation scheme; for each message element, measure afirst branch amplitude and a second branch amplitude orthogonal to thefirst branch amplitude; and demodulate the message element by comparingthe first and second branch amplitudes to the Nlevel amplitude levels.